Defending champion Andy Murray and world No. 1 Novak Djokovic moved a step closer to a potential showdown in the semifinals of the U.S. Open, while Stanislas Wawrinka pulled off a mild upset over Tomas Berdych.

Murray started slowly in Tuesday night's final match on Arthur Ashe Stadium, dropping the first set to Uzbekistan's Denis Istomin in a tiebreaker.

But the Brit responded quickly, breaking his opponent's serve twice in the second set and then putting in a workman-like performance for the remainder of the 6-7 (5-7), 6-1, 6-4, 6-4 victory.

Murray also had luck on his side late in the fourth set.

It appeared he had missed a return of serve on break point when he hit the ball off his racquet frame, but instead it went high into the night sky and landed in the court and the Scotsman ended up winning the point.

He then served out the match in the next game.

Although the world No. 3 has struggled a bit more than expected in the early rounds, he said afterward that he felt confident about his chances and was ready to peak in the tournament's final rounds.

"I think now hopefully I'll start playing a little bit better from now on ... I'm in the quarterfinals of a Slam. It's not an easy thing to do, and the matches are going to get tougher. I'll have to up my game," Murray said.

The Scotsman also joked on Twitter about his lucky shank in the penultimate game of the match.

"I hit the luckiest tennis shot of my life this evening #shank #grease but what is the saying about luck and working hard?" Murray wrote.

Next up for the Brit in Thursday's quarterfinals will be Swiss Stanislas Wawrinka, who surprised Czech Tomas Berdych 3-6, 6-1, 7-6 (8-6), 6-2.

Djokovic, meanwhile, cruised into the tournament's final eight with a 6-3, 6-0, 6-0 shellacking Tuesday of Spain's Marcel Granollers, while Russia's Mikhail Youzhny outlasted Australia's Lleyton Hewitt 6-3, 3-6, 6-7 (3-7), 6-4, 7-5.

Murray and Djokovic could meet in Saturday's semifinals in what would be a rematch of last year's title match, which the Scotsman won in five sets for his first Grand Slam title.

The top-ranked women's players also advanced on Tuesday, with American No. 1 seed Serena Williams trouncing Spain's Carla Suarez Navarro 6-0, 6-0, Chinese No. 5 seed Na Li overcoming a second-set hiccup to defeat Russia's Ekaterina Makarova 6-4, 6-7 (5-7), 6-2, and No. 2 seed Victoria Azarenka of Belarus rallying to top Serbia's Ana Ivanovic 4-6, 6-3, 6-4.

Williams and Li will meet in Friday's semifinals, while Azarenka is scheduled to play her quarterfinal match on Wednesday evening against Slovakia's Daniela Hantuchova.

Wednesday's other women's quarterfinal will be an all-Italian matchup pitting Roberta Vinci against Flavia Pennetta.

In men's quarterfinal action Wednesday, Spain's David Ferrer will take on France's Richard Gasquet and world No. 2 Rafael Nadal of Spain is scheduled to square off against countryman Tommy Robredo, who stunned five-time champion Roger Federer on Monday. EFE