James Blake returns a shot to Juan Martin Del Potro in their round-robin match in the Tennis Channel Open on Thursday. Blake won after Del Potro retired in the second set. Photos by John Locher. Juan Martin Del Potro sits as a trainer examines him during his match with James Blake at the Darling Tennis Center. Del Potro later retired, citing respiratory distress, with Blake leading 6-1, 3-1. After hours of discussion, ATP officials decided to rescind a round-robin rule, allowing Blake to advance from Group 1.

First he was in. Then he was out. Then he was back in.

In a bizarre set of circumstances Thursday, James Blake, the Tennis Channel Open's top seed and defending champion, went from advancing to today's quarterfinals to being eliminated in a matter of seconds, then being placed back in the tournament three hours later.

Entering his final round-robin match at the Darling Tennis Center, Blake needed to defeat Juan Martin Del Potro in straight sets and hold him to five or fewer games won. He was well on his way to doing so, winning the first set 6-1 and leading the second 3-1 when Del Potro retired, citing respiratory distress.

By rule, Del Potro's retirement meant his record did not count in Group 1. That meant either Blake or Evgeny Korolev would advance to single elimination in the three-man group.

And because Korolev beat Blake 6-2, 6-4 on Tuesday, he should have advanced to the quarterfinals.

But Blake and Del Potro said they did not know the rule and that it wasn't explained to them before their match.

A lengthy discussion ensued between the players, tournament officials and the ATP, and a conference call was placed from Las Vegas to London and Acapulco, where ATP officials joined the conversation.

Late in the day, the ATP announced it was rescinding the rule, even though the tournament was in its fifth day. Three hours after he had left Stadium Court, Blake was back in and Korolev was out.

"A mistake was made, and the ATP is correcting a mistake," Blake said. "Maybe I'm biased, but I think it's a fair decision."

Blake joins Sam Querrey, Jurgen Melzer, Jan Hernych, Fernando Verdasco, Feliciano Lopez, Lleyton Hewitt and Marat Safin in the final eight.

Blake will meet Querrey at noon today in a match between the two remaining Americans. Blake defeated Querrey last year at Indian Wells, Calif., in their only meeting.

In a statement issued by ATP executive chairman and president Etienne de Villiers, the organization said its decision to change the rules was dictated by common sense.

"This has troubled me enormously, and I feel as though I'm damned if I do and damned if I don't," de Villiers said. "We have said all along we are going to learn from the experiment. A similar situation occurred in Buenos Aires, which has given us great cause for concern. It is clear our fans like round robin, and research confirms that. But unless we can find a way to ensure that withdrawals don't unfairly affect the outcome of groups, I'm afraid round robin will fail.

"James Blake will be awarded the group on the basis that the rules were not sufficiently explained. James was within a few games of winning the match comfortably to advance. Juan Martin has stated that he would have completed the match had he been fully aware of the implications of his retirement."

Del Potro said: "I wanted to finish the match. But I was not aware of the technicality of the rule. I did not feel comfortable continuing."

Tour officials said the round-robin format will be reviewed in three weeks at a board meeting in Miami.

The ruling gave tournament director David Egdes his star attraction for at least one more day.

"We're obviously thrilled James is still in," Egdes said. "But James isn't the lone ticket-seller. We have other top players here that the fans want to see.

"We would have been OK with it had Korolev been in. You have to understand, we're not the decision-maker here. We're just abiding by the rule that was handed down."

Korolev refused comment, but he could not have shared in Egdes' enthusiasm despite leaving with some prize money.

The ATP awarded him $11,375 (the average amount of prize money from the quarterfinals and semifinals). He normally would have received $6,450 for his round-robin performance.

Hewitt, the No. 2 seed, said Korolev seemed upset in the locker room and questioned the ATP's decision.

"I saw what was unfolding and I'm mystified by the ruling," Hewitt said after rallying to defeat Thomas Johansson, 4-6, 7-5, 6-2. "I don't see how they can change the rule in the middle of the tournament. That's not right.

"If I was (Korolev), I'd be pissed off. This is a kid on the rise. He beat Blake 2 and 4 the other night. The money's not going to matter to him. I feel sorry for the bloke."

Blake said he also felt bad for Korolev to a certain extent.

"If I was Korolev, it would be a tricky situation," Blake said. "But at the end of the day, it's about who would have been wronged more."

Blake knew he had little margin for error Thursday, and he played every point that way. Using a stinging forehand, he kept Del Potro pinned on the baseline, opening up the rest of the court for himself.

Blake went up an early break in the first set and, despite giving it back at 2-0, broke back at love to lead 3-1. He scored a third service break to go up 5-1, then closed out the set by holding serve.

"It was very different, very strange," Blake said of his situation. "My main goal was to get out fast, and I tried to put pressure on him."

By losing just the one game, Blake had given himself some wiggle room. Or so he thought. If he won the second set 6-4 or better, he would advance to the quarterfinals.

But the one scenario he didn't consider was about to surface.

Blake again started quickly, securing an early break in the first game. The two then exchanged breaks, giving Blake a 2-1 lead.

During a changeover, Del Potro said he was having trouble breathing and called for a trainer. He was examined and decided to continue.

Del Potro had Blake in trouble at 30-40 but slipped, and Blake won the point. He eventually held with a 118 mph ace to lead 3-1.

Del Potro then quit. Little did he realize it at the time, but his decision set off a firestorm that will rage for weeks as the ATP decides what to do with the popular yet controversial round-robin format.

"With any new system, there are going to be flaws, hiccups," Blake said. "We're learning as we go along. I'm sure it will be a hot topic of discussion in three weeks in Miami."