Kevin Na was in the driving seat to advance from Group 6 as day three of the WGC - Dell Technologies Match Play got under way at Austin Country Club.
The American had two wins from his first two matches, meaning he required just a half from his clash against Chris Wood, and he was two up at the turn against the already eliminated Englishman.
Russell Knox was two down after 12 holes against Danny Willett - a result that would end his chances in Group 11 - while Lee Westwood was all square against Pat Perez after six holes in a Group 3 match he had to win.
Na took advantage of a bogey-double-bogey from Wood to quickly move two up and birdies on the fourth and sixth had the new European Tour Member in total control.
A bogey on the eighth saw him drop back and when Wood birdied the ninth, the door was still slightly ajar for Matthew Fitzpatrick and Justin Thomas.
Should Wood beat Na, the winner of their match would advance to a play-off and Thomas won the ninth and tenth to go two up.
Willett won the first against Knox with a birdie but the Scotsman evened things straight up on the next before Willett birdied the seventh and eighth. Knox hit back with a birdie of his own on the tenth but Willett had found some form and re-established his two-shot advantage at the next.
That was good news for Bill Haas, who was one up through 11 against K.T. Kim, with a win earning him a play-off against the South Korean.
Westwood had gone one up with a birdie on the fifth against Perez but the American hit straight back on the next. A Westwood win is the only result that does not see Perez go straight through, and would produce a three-man play-off with Marc Leishman.
In Group 14, Phil Mickelson was cruising into the last 16 at four up after eight holes against JB Holmes, with Si Woo Kim one up after seven against Daniel Berger.
