Andy Roddick howled in disgust at his errors, saw some of his best serves returned past him for winners and appealed to the heavens for intervention at Washington's Legg Mason Tennis Classic last night. But he slogged through three sets of alternately brilliant and errant shot-making to defeat Juan Ignacio Chela and advance to the tournament's quarterfinals.

Roddick's 6-4, 6-7 (7-4), 6-4 victory sets up a battle of the tournament's biggest servers today, with Roddick, who holds the sport's record for fastest serve, taking on 6-foot-10 Ivo Karlovic of Croatia, who fired 14 aces en route to his 7-6 (7-4), 6-2 defeat of Greg Rusedski, the last British player remaining in the draw.

This afternoon's Roddick-Karlovic quarterfinal will be a reprise of June's grass-court final at the Wimbledon tune-up at Queen's, in which Roddick never managed to break Karlovic's massive serve but won the match in two tie-breakers.

"I said then, and I wasn't far off, that it was going to be pretty boring," Roddick said after his 2-hour, 8-minute match against Chela. "It's going to be his serve and my serve. Basically it's going to come down to a couple points here and there. Besides the serve, I like my chances. But he definitely controls matches with his serve. It's probably the biggest weapon in tennis."

Today's first quarterfinal will pit Thailand's Paradorn Srichaphan, who defeated South Africa's Wesley Moodie, 6-3, 7-6 (7-1) yesterday, against Luis Horna of Peru. Horna earned the berth with a tough victory over American Robby Ginepri, who entered the Legg Mason leading the point standings in the U.S. Open Series, but fell to Horna, 6-4, 7-6 (10-8).

The evening session features Tomas Berdych of the Czech Republic, a 7-5, 6-2 victor over eighth-seed Sebastien Grosjean, against American Bobby Reynolds, a wild card who ousted Jan Hernych, 2-6, 6-4, 6-3. Arnaud Clement of France booked his spot in the quarterfinals with a 4-6, 6-3, 6-4 victory over Gilles Muller. Clement will face American James Blake, the tournament's 2002 champion, a 6-3, 6-3 winner over Tomas Zib of the Czech Republic.

Yesterday's featured match, between Roddick and Chela, was well worth sweating through the hottest day of tennis this week.

At 6-3 Chela stands an inch taller than Roddick and has a potent serve of his own. He's also the rare Argentine whose game excels on hard courts. And their first set was a duel of serves, with Roddick fending off two break points in the set and Chela managing to hold his serve until 4-5. It was a bad time for a sloppy game, and a rash of errors by the Argentine handed the next game, and ultimately the set, to Roddick.

The second set unfolded much as the first. Roddick won three service games at love, while Chela held serve with a bit more work. With a chance to close the match at 6-5, Roddick smacked a backhand into the net and another wide. The errors enabled Chela to knot the score and force a tie-breaker, and Roddick groaned in disgust.

The Argentine got the critical mini-break by ripping a return of one of Roddick's best serves for a winner. He followed with an ace and a service winner to win the tie-break and level the match at one set each.

"I wasn't happy," Roddick said flatly, asked how he felt after letting the set slip away.

Roddick emerged for the third set with a fresh shirt and new resolve, breaking Chela in the third game to take a 2-1 lead.

But the Argentine hung in, yanking Roddick around the court with drop shots and lobs. Roddick thrilled the crowd with his effort and rewarded himself with a clenched fist for each point he won after racing full-out to retrieve a shot.

"Tonight is the kind of night where you feel you're on the verge of playing well, but then I'd throw in some errors," Roddick said afterward.

"It was one of those see-saw matches that you kind of fight through and win stuff you feel is maybe not your best."

Roddick readily conceded he'll have to do better today against the towering Karlovic, whom he described as serving "out of a tree."

"You can't teach being 6-foot-10," Roddick said, asked how Karlovic's serve compared to that of the game's other big servers, such as Rusedski and Marat Safin. "The angles that he's able to create, being 6-10. You're hitting returns above your head, whereas normally your hitting them by your hips. You have to hope a little bit on his serve and really bear down if you do get an opportunity."

Few did at Queen's, where Karlovic held his serve on 65 of 66 service games played during the tournament.

Through the first seven months of the season, Karlovic leads all players in points won on his first serve (82 percent), according to ATP statistics. Roddick leads all player in percentage of service games won (92); Karlovic and top-ranked Roger Federer are tied for second (90).

Karlovic had nothing but compliments for Roddick's serve, which he called one of the best in the game. Asked what he recalled about their recent grass-court meeting, Karlovic said: "It was my first final, so I was a little bit overwhelmed at the whole atmosphere. It was still a close match, so here it should be also close. An interesting match."

Andy Roddick, serving during his three-set triumph over Juan Ignacio Chela, next faces 6-foot-10 Ivo Karlovic.