KEY BISCAYNE, Fla. (AP)—The stadium erupted when Mardy Fish walloped the final shot of the match for a winner, and he let loose a jubilant roar of his own.

The American earned one of the biggest victories in his 10-year career Saturday at the Sony Ericsson Open, where he upset 2009 champion Andy Murray 6-4, 6-4.

Fish repeatedly came through with big serves at key moments, while Murray went into a funk after he frittered away an early lead. The Scotsman was the Australian Open runner-up in January and was seeded No. 3 at Key Biscayne but failed to survive his opening match.

“He probably didn’t play the way he did in Australia,” Fish said. “But I don’t care.”

Murray confirmed he has been struggling the past two months and described the problem as mostly mental.

“It’s purely down to me, what goes on inside my head,” he said. “It doesn’t matter how well you practice. You need to be tough in the matches.”

Top-ranked Roger Federer held every service game and won his opening match by beating lucky loser Nicolas Lapentti 6-3, 6-3. Federer, the Key Biscayne champion in 2005-06, has an inviting path to the final with Murray out. No. 2 Novak Djokovic was eliminated Friday.

“I hadn’t even started playing yet, and there are two big names out of the tournament already,” Federer said. “It worries me as well, being the top seed. I’m relieved I’m through the first match.”

Rafael Nadal will overtake Murray for the No. 3 spot in the next rankings, while Fish advances to the third round at Key Biscayne for the first time since 2003.

“I desperately wanted to play well here,” said Fish, who is from Vero Beach.

Once a top-20 player, Fish joked that declining fortunes have made him a doubles specialist. It’s true he’s playing doubles at Key Biscayne, but he’s also mounting a comeback from left knee surgery last September.

Fish’s ranking of 101st will rise thanks to his second career win over a player ranked in the top three. He beat Federer at Indian Wells two years ago.

While U.S. tennis fans could boast about the upset, their lone remaining hope on the women’s side also advanced. Three-time champion Venus Williams reached the fourth round by beating Roberta Vinci 6-1, 6-4.

Williams is the only American who reached the final 32 in the women’s draw. She and sister Serena are the lone U.S. women in the top 40.

“It’s just definitely strange because of the unbelievable tradition we’ve had with tennis for Americans since the beginning,” Williams said. “That’s what makes it so odd. With Serena and me, the standard has been set pretty high. Hopefully there will be someone coming along soon with the tools and the traits, and who will build that in their game to get there.”

Serena has been sidelined with a knee injury since winning the Australian Open in January. She’s working out this month with fitness guru Mackie Shilstone but withdrew from the tournament before the start.

While Serena is ranked No. 1, Venus is the hottest player on the women’s tour—not necessarily because of the red corset she unveiled this week, but because she has won 12 consecutive matches. The winning streak includes three victories after losing the first set.

“I’ve come from down, up, around and over,” she said. “Being on a winning streak helps my confidence every time.”

Top-seeded Svetlana Kuznetsova beat No. 27 Agnes Szavay 6-2, 6-3. Former No. 1 Ana Ivanovic’s recent struggles continued with a loss to No. 6 Agnieszka Radwanska, 7-5, 7-5.

Joining Fish in the third round were No. 5-seeded Robin Soderling and No. 10 Fernando Verdasco. Soderling beat Peter Luczak 7-6 (5), 6-0, and Verdasco eliminated Dudi Sela 6-1, 6-2.

Murray trains in nearby Miami, and he became the first British player to win Key Biscayne when he beat Novak Djokovic in last year’s final. But the Scotsman said he sensed trouble against Fish, even serving with a 3-1, 40-love lead.

The tide turned when Murray lost that game.

“I just wasn’t very good today, and I’m going to need to get a lot better,” he said. “If you leave the ball short in the middle of the court, it’s very easy for guys to attack and be aggressive.”

Fish lost just six points on his first serve. He hit 28 winners to Murray’s nine and frequently charged the net behind returns.

“Playing a guy like Andy, I needed to stay aggressive,” Fish said. “I’m just not going to win the points very often if they go 10 shots in a row.”

Murray went only 1 for 5 converting break-point chances, but he wasn’t at fault. Fish hit several unreturnable serves in those situations.

“You’ve got to go in thinking you can actually win,” Fish said. “That helps.”