Argentina's Juan Martin del Potro advanced to the semifinals of the Olympics men's tennis singles tournament with a 6-4, 7-6 (7-4) victory here Thursday over Kei Nishikori and now is one win away from a spot on the podium.

The world No. 9 and first-time Olympian needed one hour and 55 minutes to defeat his Japanese rival, who had upset fifth-ranked Spaniard David Ferrer in the previous round.

The first set was an up-and-down affair in which Del Potro lost his own serve twice but was still able to take the set 6-4 by breaking Nishikori's serve on three occasions.

Japan's top-ranked player only managed to win 56 percent of his first-serve points that set and just one of eight second-serve points.

In the second set, Del Potro raced out to a 5-2 lead and served for the match at 5-3. He lost that game due in part to a double fault but was able to regroup and take the match in a tiebreaker.

"The match was tough to the end. We broke each other a lot of times. That's why what I did in the second set (grabbing a break of serve lead) wasn't definitive. I made errors that I almost paid for dearly but I was able to get myself back in the match," the 23-year-old Del Potro said in the post-match press conference.

Del Potro avoided a nemesis when Nishikori defeated Ferrer, who has defeated the Argentine in their past three matches; the last of them was a straight-set victory last month at Wimbledon, also the venue for the Olympic tournament.

But a much more imposing rival looms Friday in the form of world No. 1 and 17-time Grand Slam champion Roger Federer, who has won all five of his matches against Del Potro this year and continued his strong recent run of form Thursday by defeating big-serving American John Isner 6-4, 7-6 (7-5) in another quarterfinal.

"Once again against Federer. I'm calmly doing my job. It's no small thing to be among the four best and to battle the world's best. It's very important. I'll try to put up a fight," Del Potro, who defeated the Swiss great for his lone Grand Slam title - the 2009 U.S. Open -, said.

Looking ahead, Del Potro is well aware of the challenge that he faces in trying to win a medal for Argentina. If he fails to pull off a big upset on Friday against the Swiss on his beloved grass, he would have to defeat either world No. 2 Novak Djokovic of Serbia or world No. 4 and crowd favorite Andy Murray of Britain for the bronze.

"The opponents are very difficult. They're the world's best. The three best and me and I want to enjoy it. I'm close and I want to keep battling," Del Potro said.

In other men's singles quarterfinal action Thursday, the last remaining Spanish player, Nicolas Almagro, bowed out of the competition with a 6-4, 6-1 loss to Murray.

Almagro had rolled through his first three matches, scoring straight-set victories over Serbia's Viktor Troicki, Russia's Alex Bogomolov Jr. and Belgium's Steve Darcis, but he proved no match for the grass court prowess of Murray, who entered the tournament fresh off a runner-up finish at Wimbledon.

The serve was a major factor as Murray struck 15 aces to just one for Almagro. The world No. 4 not only served with power but also accuracy, putting in a whopping 81 percent of his first serves throughout the one-hour, nine-minute match.

The marquee contest of the men's singles quarterfinals pitted Djokovic against dangerous Frenchman Jo-Wilfried Tsonga.

In a rematch of their Wimbledon semifinal encounter in 2011, also won by Djokovic, the Serb ran away with the first set and then snagged a crucial break of serve late in the second set to secure a 6-1, 7-5 victory.

In the men's doubles, the Spanish duo of David Ferrer and Feliciano Lopez kept alive their country's hopes for a tennis medal with a 6-4, 6-4 victory over Croatia's Marin Cilic and Ivan Dodig.

Spain has only managed two medals thus far in the Olympics - swimmer Mireia Belmonte Garcia's silver in the women's 200m butterfly and slalom canoer Maialen Chourraut's bronze in the women's slalom K-1.

The Iberian nation has had a lot of recent success in tennis but most of it has been achieved by Rafael Nadal, the defending Olympic singles champion, who decided not to defend his title due to lingering knee problems.

Argentina has won three Olympic tennis medals overall, including a women's singles silver captured by Gabriela Sabatini in the 1988 Seoul Games. EFE