Mark Ein, owner of the Washington Kastles, photographed at the top of Kastles Stadium near the waterfront. Ein believes the Kastles can be “an anchor” for fun in the District. (Toni L. Sandys/THE WASHINGTON POST)

The season’s championship was at stake, as was the Washington Kastles’ 31-match winning streak. So a few hours before Venus Williams was to lead the squad into the 2012 World TeamTennis title showdown in Charleston, S.C., its anxious owner, Mark Ein, asked Williams’s elder sister whether there was anything his star player might want.

“Green juice,” Isha Price replied.

Few restaurants were open on a sleepy summer Sunday in Charleston — certainly none serving the pulverized medley of kale, cucumber and wheat grass that Williams loved before important matches.

At Ein’s behest, a Kastles staffer contacted Williams’s nutritionist for the recipe, worked the phones until finding a restaurant with a chef willing to whip it up and sped off on the 90-minute round trip. Just before Williams strode on court, Ein surprised her with the special concoction.

Williams led the Kastles to their second consecutive WTT title that day and was paraded around court atop her teammates’ shoulders for her MVP heroics. While it’s doubtful the green juice sealed the outcome, Ein’s zeal to procure it offers a window on the lengths the Washington-based venture capitalist will go to ensure the success of the sporting start-up he launched in 2008.

Ein played for the team at Bethesda-Chevy Chase High in the early 1980s. (Ein Family Photo/EIN FAMILY PHOTO)

“He’s actually the perfect owner,” said Billie Jean King, 69, former tennis champion and sports pioneer who co-founded the coed professional WTT league in 1974. “He loves tennis. He gives a lot back to the community. He’s involved in education, the arts and the fabric of the city. That’s what you want in an owner.

“More importantly, he never stops thinking about the team.”

‘Courting history’ (sort of)

Though the Kastles have yet to turn a profit, Ein, 48, said their bottom line is trending in the direction that any investor who takes a long-term view wants to see, with expenses shrinking and revenues on the rise.

On the court, the Kastles have proved a winning machine, claiming three WTT championships in five seasons and compiling back-to-back undefeated seasons.

That streak will be on the line when the squad opens its 2013 season Monday at Kastles Stadium on the Wharf against the New York Sportimes. With a victory and another Tuesday against the Boston Lobsters, the Kastles’ winning streak would reach 34 matches.

And that, as Ein has touted for months, would surpass the 1971-72 Los Angeles Lakers’ string of 33 consecutive victories, hailed as the longest winning streak in the history of professional sports.

An audacious comparison?

“Comparing a World TeamTennis winning streak with that of the Los Angeles Lakers of 1971-72 — or any other streak like that in major league sports — is rather ludicrous,” said Marc Ganis, president of Chicago-based Sports Corp consulting firm. “It’s a lovely way to bring attention to the team. But the streaks are simply not comparable in terms of the competitive level of the sports. What’s going on in World TeamTennis is fairly unknown to most people on the planet.”

World TeamTennis has done well to survive nearly four decades, given its lack of significant TV revenue. But it has yet to find a broad-based audience, and traditionalists view it as bordering on an exhibition rather than white-knuckled competition.

To Ein, it is every bit a major league sport, though its 14-match regular season runs just three weeks compared with the NBA’s 82-game, six-month regular season.

But Ein, a 1982 graduate of Bethesda-Chevy Chase, where he was captain of the tennis team, has never lacked for pluck, spurred by outsize belief since childhood.

His first entrepreneurial enterprise came just before seventh grade, when he and his friends at Rollingwood Elementary learned the coach of their soccer team, the Chevy Chase Chargers, was moving back to California and the squad would be disbanded.

“No one would pick up the mantle of keeping the team alive,” Ein recalled. “We were about to start seventh grade, and I said, ‘There is no way I’m letting this thing die!’ ”

So Ein took on all front-office duties. He found a new coach, reserved practice fields and coordinated the paperwork with players’ parents to keep the Chargers going.

That spirit informs Ein’s professional life today. He has promoted his Kastles’ streak as closing in on that of the Wilt Chamberlain-era Lakers not with a wink and a nod but in earnest. “To me,” Ein said, “it is, in many ways, more similar to than it is different than the Lakers.”

To that end, Ein has financed a 25-minute documentary, “Courting History: The Winning Streak of the Washington Kastles,” that chronicles the seriousness with which his team approaches its matches and the teamwork behind its success. The film opens with archival footage of the 1971-72 Lakers to set the stage.

“It’s great for the league,” King said of the Kastles’ streak. “It’s getting us a lot of mileage we wouldn’t get.”

‘An anchor’ in D.C.

The son of an allergist, Ein was 4 when his family moved from New York to the Washington area. He graduated from Penn’s Wharton School with a degree in economics, worked for Goldman Sachs in New York for three years, followed by a stint with a West Coast venture capital firm. After Harvard Business School, he returned to Washington in 1992 to work for the Carlyle Group. In 1999, he set out on his own.

It’s difficult to gauge Ein’s personal wealth, which he prefers to keep private. But as an investor and entrepreneur, he has played a role in founding, acquiring or backing five companies worth more than $1 billion, according to his official biography.

He acquired Kastle Systems, a leading provider of office-building security, for which the WTT team is named, in 2007.

He briefly considered joining Chevy Chase native Josh Harris, a longtime friend, in his bid to buy the NBA’s Philadelphia 76ers but decided against it, preferring to invest in Washington.

Only after attending his first WTT match did it pique his interest. He arranged a meeting with King during the 2007 U.S. Open. And after studying the business model and reflecting on Washington’s summertime offerings, he went forward.

“It entered my mind like an entrepreneurial spark,” Ein said. “I thought I could use it as an anchor, to create a center of fun activities in Washington.”

From the outset, Ein envisioned staging the Kastles’ home matches downtown. The team first played in 2008 in a temporary stadium at the former site of Washington’s convention center. In 2011 it moved to the 2,700-seat Kastles Stadiuim in Southwest Washington.

Ein also wanted its roster, as well as its fan base, to reflect the city’s diversity. To that end, he has worked with the Washington Tennis & Education Foundation to make it possible for youngsters from less privileged parts of the city to attend matches, receive free rackets and take part in clinics with Kastles players.

Paying an undisclosed fee to acquire the rights to sign Serena Williams and later Venus was an integral part of jump-starting broad-based interest in the team.

“If you really want to make the team a community platform that brings people together, there is no one better than Serena and Venus, who demonstrate the power of sport to change lives, having grown up in Compton and created the lives they have,” Ein said.

While Serena Williams isn’t playing for the Kastles this season, India’s Leander Paes returns, as does Russian-born Anastasia Rodionova. Former world No. 1 Martina Hingis of Switzerland will play selected matches as well.

“It’s fun to build something, to create something and be involved at a pretty detailed level,” Ein said. “This is a pure start-up. And behind most start-ups is someone who sees a need and has a vision for how it could be filled. To some extent, our customer is me as a kid. I know that kid, and I know what that kid and that family are going to want.”

Still an avid player, Ein is a frequent doubles partner of former touring pro Richey Reneberg, 47, a Bethesda resident and former world No. 1 doubles player who won the 1992 U.S. Open doubles title.

“Mark’s a very good player and very competitive,” said Reneberg, who works for a New York-based investment firm. “Even on days when it’s cooler or windy and conditions aren’t perfect, he’s always 100 percent in it. In everything he does, he has fanatical energy.”

As a tennis fan, that includes traveling to tournaments across the country and Europe, as his schedule permits, to cheer on members of the Kastles.

And as a WTT owner, it means obsessing over details — from helping drape free Kastles T-shirts over each seat in the stadium to providing an emergency flight home for a player with an ailing parent.

“Nobody invests more in their team — not just financially but from the heart,” said 1993 French Open doubles champion Murphy Jensen, 44, the Kastles’ voluble coach. “That’s Mark Ein. He’s the guy that’s calling me at 3 o’clock in the morning, inspired by something another team is doing and saying, ‘We’ve got to raise the bar!’

“And it rubs off. No front office, no set of interns, no set of fans post up like ours! There is nothing that he won’t give his team, professionally or personally, to be successful.”