Novak Djokovic sent second-seeded Spaniard Rafael Nadal packing on Wednesday while Andy Murray advanced courtesy of injured third seed Andy Roddick at the US$6.9 million Sony Ericsson Open.
Djokovic, the 10th seed, avenged his loss to Nadal in the final of the ATP Masters Series tournament at Indian Wells earlier this month with a 6-3, 6-4 triumph that he called the most important of his career.
He booked a clash with his fellow 19-year-old Murray, the 12th seed from Scotland, who moved on when Roddick retired late in the first set.
"Certainly I have to say that this is the biggest, and probably the most important victory in my career, and he's the best player I ever won against," said the delighted Djokovic, who claimed his first win over Nadal in three meetings.
Djokovic saved three break points in the final game before closing out the match with an ace after one hour and 37 minutes.
Nadal followed world No. 1 and top seed Roger Federer of Switzerland out of the tournament.
Federer was shocked in the fourth round by Argentina's Guillermo Canas, the same player who ended his 41-match winning streak in the second round at Indian Wells.
Canas was to bid for a semi-final berth yesterday when he was to take on sixth-seeded Spaniard Tommy Robredo, while seventh-seeded Croatian Ivan Ljubicic was to take on Argentina's Juan Ignacio Chela.
Nadal, 20, was philosophical.
"The world is not just Federer and me," he said. "There's a lot of good players."
Murray, who was nursing a sore ankle when he lost to Djokovic in the semi-finals at Indian Wells, led 5-3 after 29 minutes when Roddick pulled out.
The US player had taken treatment before the final game in an ultimately vain attempt to continue.
"I think the medical term is `the bottom of my ass hurts,'" said Roddick, who suffered a strain to his upper left hamstring.
"He hit a volley behind me and I kind of lunged at it and jarred something. More and more it started becoming like a sharp pain and then I started feeling it even when I was just kind of cruising around the court, not even in points," he said.
Murray said he was sorry to see the match end that way.
"I guess anybody would rather get off the court quicker than longer, but I'd rather it was in normal circumstances," he said.
It will be the fifth semi-final of the year for Murray, who won at San Jose and lost in the Doha final as well and reached the semi-finals at Indian Wells and Memphis.
The injury is another setback for 24-year-old Roddick, who has yet to claim a title this year.
On the women's side, 13th seed Serena Williams followed up one shockingly easy victory with another as she dispatched eighth-seeded Czech Nicole Vaidisova 6-1, 6-4.
Williams, who had reprised her Australian Open finals rout of Russian Maria Sharapova in the fourth round, booked a semi-final clash with Israel's Shahar Peer. Peer, the 14th seed, defeated Tathiana Garbin of Italy 6-0, 6-3 to reach her first career Tier I semi-final.
The other semi-final will match world No. 1 Justine Henin of Belgium and Russia's Anna Chakvetadze.