Masters Tournament champion Jordan Spieth quickly gained the upper hand in his must-win clash with Lee Westwood in the WGC-Cadillac Match Play in San Francisco.
Spieth and Westwood had both won their first two group matches at TPC Harding Park, meaning Friday's contest between the Ryder Cup rivals would decide which player advanced to the last 16.
And World Number Two Spieth drew first blood with a birdie on the par-five opening hole before a par was good enough to win the second, where both players found sand off the tee but only Spieth was able to get up and down.
Only two of the 64 players had already booked their place in the last 16, Rickie Fowler and John Senden advancing with a match to spare thanks to victories on the opening two days against the two players who could possibly match their overall record.
Head-to-head results would decide the group winner in the event of two players finishing tied, but eight of the groups could see a three-way tie which would result in a sudden-death play-off.
The outcome was easier to predict elsewhere, with Spieth and Westwood in one of four groups to be decided by a showdown between players with a 2-0 record.
World Number One Rory McIlroy was up against FedEx Cup winner Billy Horschel, while two-time Masters champion Bubba Watson took on the man he beat in a play-off at Augusta in 2012, Louis Oosthuizen.
Former US Open Champion Webb Simpson and Gary Woodland - the bottom two seeds - did battle in group 11, with Woodland one up after 11.
Justin Rose briefly kept his hopes alive by claiming his second victory in succession with a 2 and 1 win over Ryan Palmer, only to see first-day conqueror Marc Leishman win Group 6 with a 3-0 record by beating India's Anirban Lahiri on the 18th.
Former champion Hunter Mahan also advanced to the knockout stages with his third win, the American defeating compatriot Matt Kuchar 5 and 4 in Group 14, where Scotland's Stephen Gallacher was one up after 13 against Ben Martin as he sought a consolation win.
Westwood had taken advantage of a rare bogey from Spieth to reduce his deficit on the sixth and a birdie on the ninth got the 42 year old back to all square against an opponent half his age.
