Forward Martell Webster (16 points) is one of five Wizards to score at least 14 points Wednesday in Boston. Meanwhile, Jan Vesely (center) has 2 points and 3 fouls in 13 minutes. (Elise Amendola/Associated Press)

The Washington Wizards made this offseason about adding more veterans to shepherd along their unseasoned pups, but with his team in a tightly contested battle against the championship-tested Boston Celtics on Wednesday night, Coach Randy Wittman had to go with the players who were battling, scrapping and unwilling to give in.

That meant that after forcing overtime against the Celtics, Wittman would rely on a 19-year-old shooting guard; a third-year forward who has rarely, if ever, seen a double-team; a second-year forward who played 18 seconds in the previous game; a sixth-year veteran who spent the past two seasons battling back problems; and a fourth-year point guard who entered the season with just three career starts.

Despite long odds — and only seven free throw attempts compared to 34 for their hosts — the Wizards managed to keep the Celtics on edge for most of the night. Ultimately, however, sloppy play in the final minutes of regulation and overtime contributed to a 100-94 loss at TD Garden.

“We’ve got to learn to play down the stretch,” Wittman said after the Wizards (0-3) lost both ends of a home-and-home series against Boston. “It’s a learning process, taking care of the ball, execution, making plays. It’s disappointing that we lost, but . . . a lot of good things.”

Emeka Okafor and Trevor Ariza, two of the most experienced players on the roster, sat the entire fourth quarter for the second game in a row and Wittman didn’t look to either in the extra frame.

Instead, the Wizards rode skilled big man Kevin Seraphin, an aggressive Bradley Beal, an assertive Chris Singleton, a red-hot Martell Webster and an in-control A.J. Price. All five scored in double figures — with Seraphin, Beal and Webster each scoring a team-high 16 points and helping the Wizards score more than 90 points for the first time this season.

But lacking an established go-to player down the stretch with John Wall and Nene still sidelined with injuries, and with Seraphin unable to handle a double team and Jordan Crawford hobbled by a sprained left ankle, the Wizards got careless and unraveled in the final five minutes.

Webster made a long jumper to tie the score at 92, but Brandon Bass scored five consecutive points, including a breakaway dunk that gave the Celtics a 97-92 lead with 37.7 seconds remaining.

“Our fight, our grit. Determination. We got that. It’s not too much a difference between us and them,” said Price, who had 15 points, seven assists and six turnovers. “Even though it’s my fourth year, this is still my first time closing out a game that has meaning and everything like that. I’m learning on the fly and I have to do a better job.”

Seraphin was expecting to attract more attention after surprising the Celtics with a 19-point outburst in his season debut, an 89-86 home loss to Boston on Saturday. To his surprise, Seraphin found himself unguarded for several jumpers on Wednesday, but he also made contested jump hooks. He was effective in drawing double teams but wasn’t nearly as efficient in the rematch, and after he dunked to tie the game at 80, the Celtics made him into a turnover machine.

“When they start to double-team you, that’s respect. That means that you can do something,” said Seraphin, who finished Wednesday’s game with six turnovers. “I never been in this situation. Now I have to learn, watch some video and figure out how to play with it.”

Beal was moved to tears after going without a field goal in five attempts in the previous game. With three days to ponder his struggles, he came out determined to play with more passion and purpose. He didn’t shoot particularly well — 6 for 15 — but he didn’t appear overwhelmed as he coolly came around a screen and knocked down a three-pointer that gave the Wizards an 83-82 lead late in regulation.

“It was a big shot, but there were other plays we needed to make to win the game,” Beal said. “We know they’re vulnerable. They’re an aggressive team, but they’re a lot older than we are, so we just try and wear them down.”

The Wizards were unable to complete the upset after three inexplicable turnovers on the subsequent possessions — Seraphin committed an offensive foul, then lost the ball getting trapped dribbling with his back to the basket at the three-point line before Webster attempted to go one-on-one. The Celtics didn’t make Washington pay, however, turning the blunders into just four points from the foul line.

Rajon Rondo (18 points, 14 assists) made a jumper to give the Celtics an 88-86 lead with 26.4 seconds remaining in regulation, but Singleton forced overtime with an emphatic, one-handed slam that had Kevin Garnett moving out of the way and silenced a stunned home crowd.

“We were right there,” said Singleton, who scored 12 of his 14 points in the fourth quarter. “This was one of the top teams the past five years and that’s good for us just to be in the games and we just got to keep going, go to the next level. Even though John and Nene are out, we still got the pieces here. I feel like the East is so wide open for everybody right now. We’ve just got to catch a wave and just ride it.”