Daunting task for Westwood
Lee Westwood faces the daunting task of beating Masters champion Jordan Spieth to reach the last 16 of the WGC-Cadillac Match Play as Rory McIlroy and Billy Horschel prepared to renew their "heated" rivalry in San Francisco.
Westwood recovered from three down after nine holes to beat Mikko Ilonen at Harding Park on Thursday, while world number two Spieth had 10 single putts in succession to defeat Matt Every 4&3 in group two.
"He is obviously playing very well and is probably the hottest player in the world at the moment, but when you are the favourite the pressure is all on you," Westwood said of Spieth, who came back from two down after five with the aid of six birdies in the next seven holes.
In group one, McIlroy and Horschel defeated Brandt Snedeker and Jason Dufner respectively to set up a Friday showdown which brought back memories of their ill-tempered clash in the 2007 Walker Cup.
"I know he is going to be amped up to play me and I am going to be amped up to play him," Horschel said. "We have a track record together and when we have played each other we've played our best golf and I would not expect anything less tomorrow."
McIlroy saw a two-hole lead wiped out by birdies from Snedeker on the 11th and 12th before securing victory with birdies of his own on the 15th and 18th.
Speaking about falling out with Horschel at the Walker Cup - where he felt the American's celebrations were "loud and obnoxious" - he told Sky Sports 4: " We are good now but back then we were both a little younger and more emotional. It was pretty heated.
"I don't think tomorrow will be quite like that but you need to win or you are going home."
Despite the change in format from straight knockout to 16 groups of four, there were plenty of high-profile exits with a day to spare as Ian Poulter, Henrik Stenson, Graeme McDowell and defending champion Jason Day all crashed out.
Poulter and McDowell could have few complaints after suffering their second straight defeat, but Stenson could be forgiven for having misgivings about the new format after seeing his win over Brendon Todd rendered meaningless.
Australian John Senden had already defeated Bill Haas in group three to advance regardless of the result of his match with Todd on Friday. A defeat for Senden and a Stenson victory over Haas would see both men with a 2-1 record, but Senden would go through due to his win over Stenson on Wednesday.
A similar scenario had earlier seen Rickie Fowler become the first man into the last 16, the American beating Shane Lowry thanks to holing a string of lengthy putts on the closing stretch.
"I feel bad to do that to him but it was nice to finally make some putts," Fowler told Sky Sports 4. "It would have been nice if we were throwing birdies at each other but my back was up against the wall and I needed to make those putts for par to keep the match going."
In the same group McDowell had lost to Harris English, while Poulter was also eliminated after losing 3&2 to Gary Woodland in group 11.
Scotland's Marc Warren would have secured his place in the last 16 with a win over Brooks Koepka, only to squander a three-hole lead with three to play before eventually losing on the 20th hole.
Former US PGA champion Keegan Bradley had been the first player eliminated when he lost his second match of the week to Bubba Watson, who will face Louis Oosthuizen in a group decider, the man he beat in a play-off for his first Masters title in 2012.
Paul Casey claimed his second win by seeing off former world number one Adam Scott on the 18th but needs another victory against Italy's Francesco Molinari on Friday to advance, while Justin Rose kept his hopes alive after birdies on the 18th and 19th to beat Anirban Lahiri.
"It's taken me 37 holes to get any lead in this championship," said Rose, who was never ahead during his opening loss to Marc Leishman, which came just three days after winning the Zurich Classic of New Orleans.
"It was a hard-fought battle and at least I have a chance of getting into a three-way play-off." For that to happen, Rose needs to beat Ryan Palmer and hope Lahiri beats Leishman.
Another three-way play-off could happen in group 15 between English pair Danny Willett and Andy Sullivan and US Ryder Cup star Patrick Reed, Willett beating Reed 2&1 and Sullivan defeating Ryan Moore 3&2. However, a win for Willett would definitely see him through with a 100 per cent record.