On Friday, Pete Sampras sat. Today, he shone, then stumbled, then got back up again and willed a doubles victory, keeping the United States alive in its Davis Cup matches against Australia. And now, there is only one question at the Longwood Cricket Club: Will he play singles on Sunday?

Sampras is supposed to be sitting again, watching as Todd Martin and Jim Courier try to pull the United States out of a 2-1 deficit in this best-of-five quarterfinal tie. But after Sampras and Alex O'Brien gutted their way through a rousing 6-4, 6-3, 3-6, 4-6, 6-3 victory over Mark Woodforde and Sandon Stolle this afternoon, both Sampras and U.S. captain Tom Gullikson strongly hinted that Sampras might take Martin's place in Sunday's match against Patrick Rafter.

"Let's be honest here, I have said the last three months [that I wouldn't play singles], but our back is against the wall at the moment, and we are going to talk about it tonight a little bit and go from there," Sampras said. "It is a very sensitive subject."

Davis Cup rules state that at this point a substitution can only be made in the case of an illness or injury. Martin said several times after his match Friday that he felt fine, and on the way to a practice session late this afternoon he told an Australian reporter, "I'm not injured; I'm fine."

When told that Gullikson had said, "Some of the players aren't 100 percent fit right now," and that he "wouldn't rule out" Sampras playing, Martin looked startled. "I haven't spoken to Gully," Martin said. "I don't want to say anything."

Gullikson later said, "If Todd says he is 100 percent ready to go, he'll probably play. But if he's dehydrated or if there is something wrong with his elbow, then we will have to look at it."

The United States has been on the verge of elimination since Friday, when Martin and Courier lost to Lleyton Hewitt and Rafter, respectively, in singles matches. Many people--including Martin--expected Sampras to be playing singles all along this weekend, but Sampras, who joined the U.S. team late, said he did not want to appear to be pushing Martin aside.

That seems to have changed now. Martin is scheduled to play Rafter in the first match Sunday. If he loses Australia will win the tie, no matter what Courier does against Hewitt later. Rafter is heavily favored; he has won five of the last six times he played Martin.

Sampras has not had a great record against Rafter either, having lost the last three times they played. But the six-time Wimbledon champion would be a much more formidable opponent than Martin, a fact not lost on Australian captain John Newcombe, who seemed stunned that Gullikson was even thinking of using Sampras.

"I am surprised because the rules say that you have to have a doctor's report saying you are not able to play," Newcombe said, grimacing.

When asked if he planned to lodge a protest, he said, "I don't know. I have never been in the position where someone has pulled out when they shouldn't."

Newcombe was just as discouraged by today's match as he was about the news about Sampras, especially after Woodforde and Stolle battled back from a two-sets-to-nothing deficit to drive the match to a decisive fifth set.

For the second day in a row, the heat on the court was suffocating--the temperature reached 129 degrees at one point, although it was hard to tell if it climbed higher because the USTA's thermometer only registered up to 130.

By the fifth set, all four players on the court were drenched in sweat, but each appeared quite alert as the stakes rose with each point.

The set stayed on serve until the eighth game, when the Americans held three break points. They finally converted when O'Brien hit a lob that went over both Australians' heads. Stolle got to it, but his return was long. The break went to the Americans, giving them a 5-3 lead.

Sampras got ready to serve out the match, and many of the fans, already on their feet, remained standing for what they assumed would be a quick game. But the Australians were not ready to leave the court, and they pushed the Americans to a break point at 30-40 when Sampras hit a forehand long. Sampras went to his chair to change his racket as a nervous buzz circled the stadium.

When he returned, he took charge. To save break point he hit a great serve, and when it was returned, he ran to the net to pound the ball out of reach. He delivered an ace on his next serve, giving the United States match point. He hit his final serve almost as hard, and although Woodforde was able to get his racket on the ball, the return went long, giving the Americans the match and keeping them alive.

"Serving for the match, I was jumping out of my skin," Sampras said.

He said, "It was a sweet victory," but remained coy about Sunday. "It is something we are going to talk about. It was a warm day, but I thought I recovered pretty well after the match. We will keep everyone posted."

Davis Cup

Matchup: United States vs. Australia.

Where: Brookline, Mass.

Score: Australia leads best-of-five quarterfinal, 2-1.

Today's schedule: United States' Todd Martin vs. Patrick Rafter, followed by United States' Jim Courier vs. Lleyton Hewitt.

TV: ESPN, 3 p.m. (tape delay).

CAPTION: Volley isn't too hot to handle for Sampras, but on-court temperature almost was: 129 degrees.

CAPTION: Pete Sampras, left, Alex O'Brien defeat Sandon Stolle and Mark Woodforde, 6-4, 6-3, 3-6, 4-6, 6-3.