The heat was the talk of the day and comebacks were the hot topic at night at the Sovran Bank/D.C. National Tennis Classic yesterday at Rock Creek Tennis Stadium.

During the afternoon session, No. 8 seed Diego Perez, leading in his match against Sweden's Johan Carlsson, was overcome by the 95-degree-plus heat and retired.

"This tournament is the hottest," said Canada's Martin Wostenholme, who also wilted in losing to No. 5 Jimmy Arias, 7-6 (7-4), 6-1. "I won the first set Monday and sat down and felt cool. Losing the first today, I knew I had an uphill battle."

Ninth-seeded Aaron Krickstein and unseeded Marko Ostoja escaped the heat, playing in the cool, breezy evening, but they also faced uphill battles. Krickstein beat Carlos DiLaura of Peru, 6-2, 3-6, 7-5, and Ostoja upset No. 7 Milan Srejber of Czechoslovakia, 4-6, 7-6 (7-5), 7-6 (7-2).

After losing the first set and the first four games of the second set, Carlsson won five consecutive games as the weary Perez sat down between points and staggered through his serves. At 0-15 of the second set's 10th game, he hit a fault on his first serve and never attempted the second as he told the chair umpire he had to quit.

"The heat didn't bother me," Carlsson said. "It's strange. It never gets any hotter than 70 degrees in Sweden."

Tournament officials said Perez, suffering from nausea, was treated by tour trainers. He was not available for comment.

Other seeded winners included No. 12 Horacio de la Pena of Argentina, downing Jimmy Brown of Largo, Fla., 6-4, 6-2; and No. 16 Fernando Luna of Spain, beating Romania's Florin Segarceanu, 7-6 (7-4), 6-4. Unseeded Dan Goldie of McLean outlasted Houston's Richey Reneberg, 6-3, 7-6 (8-6) and Jay Berger of Fort Lauderdale, Fla., defeated Patrick McEnroe, the brother of tennis star John McEnroe, 6-3, 7-5.

Marty Davis upset No. 10 Francisco Maciel of Mexico, 7-6, 7-5, 7-6 (8-6), in 2 hours 55 minutes.

"With the crowd early on, I thought was playing Mexican Davis Cup," said Davis, of Alameda, Calif., No. 74 in the world. "Maciel was such a jerk. I got angry at him a couple of times for delaying play, then the crowd started to get behind me."

"What does he expect from me?" Maciel said. "Every time he was serving, he took too long. I was really tired. I don't know why he is complaining. He won."

Serving at 5-4 in the third-set tie breaker, Maciel came to the net and swatted a forehand volley to the corner. It was called out. Maciel, who later said he didn't know if the shot was in, wanted the line checked. But he did not get that or the point.

At 5-5, Davis hit long. But he fought off a match point by zooming an ace for 6-all. Davis, returning to his serve and volley play, forced Maciel to hit into the net twice for the win.

Arias survived a grueling 1-hour 12-minute first set and then had no trouble with Wostenholme, hot and exhausted, in the second set.

"The heat here is mental," said Arias, a finalist here in 1982 and 1983. "The first set felt like the hottest one in my life. The second set felt much cooler."

It was certainly cooler by the time Krickstein, trailing, 2-5 in games and 0-15, strung together sharp backhands, bullet forehands and DiLaura mistakes for a 17-point tear that pushed him ahead to 6-5, 15-0. He ended the match with a perfectly-anticipated volley and an ovation from the stadium court crowd of 6,000.

"I just felt like if I could hit that one big shot, that one backhand," said Krickstein of Grosse Point, Mich., "I could win a few games in a row."

Ostoja came back from a 2-5 deficit in the third set and whipped through the tie breaker as 6-foot-6 Srejber hit four shots into the net. "You just have to keep him moving," Ostoja said.

Ostoja said he "went cold," leading 2-0, 0-40 after Srejber got a penalty point for fussing for five minutes over a line call. But he got hot again, saving match point at 3-5, by forcing Srejber to run the court as "I started to get everything."