Spanish fourth seed David Ferrer has matched his best Grand Slam showing by advancing to the US Open semi-finals in New York, beating Serb eighth seed Janko Tipsarevic 6-3, 6-7 (5/7), 2-6, 6-3, 7-6 (7/4).

In a marathon battle that lasted four hours and 31 minutes on the Flushing Meadows harcourts on Thursday, Ferrer rallied from 4-1 down in the final set to force a tie-breaker, then won five of the final six points of the match, the last when Tipsarevic netted a backhand.

"I'm really happy," Ferrer said.

"It was a very emotional match. It was a really tough match. Janko, he's an amazing player and he really fought a lot. He deserved to win today too."

Ferrer improved to 17-9 in career five-set matches while Tipsarevic fell to 15-8.

"It was a lottery in the fifth set," Ferrer said. "I had a break down but I was fighting also and I won. I had to fight a lot and be focused every point."

In the fifth set, Tipsarevic broke Ferrer's first service with a backhand volley winner for a 2-0 lead on the way to a 4-1 edge.

But the Serb slipped and fell on his left side going for a Ferrer backhand in the sixth game, which Ferrer held to pull within 4-2.

Ferrer, held, broke back in the seventh game, held again to pull even at 4-4 and earned two break points in the ninth game before Tipsarevic called for a trainer, having his right upper leg taped after reaching toward his right groin during a rally.

The Serb responded with a forehand volley winner and three service winners to hold and each man held into the final tie-breaker.

Ferrer v Djokovic

Ferrer will play on Saturday for a berth in the final against Novak Djokovic, the winner of Thursday's other quarter-final.

Defending champion Djokovic beat Argentine seventh seed Juan Martin Del Potro 6-2 7-6 6-4.

The second-seeded Serb gained the decisive edge in the quarter-final by winning a second-set struggle against Del Potro, who won here in 2009.

The set lasted 84 minutes and featured a 17-minute game at 6-5 when Del Potro saved three set points to force a tiebreaker.

It was tennis of the highest order as the players sent each other from corner to corner, and from net to baseline and back again.

Djokovic emerged with the set after taking the tie-break 7-3 over the seventh seed, who more than once draped himself over the net in exhaustion.

"Even though it was a straight set win, it was much closer than the score indicated. He's a great player," said Djokovic, who reached his 10th successive grand slam semi-final as he pursues a sixth slam title.