Lee Westwood maintained his excellent form by beating Matt Every to make a winning start to the WGC – Cadillac Match Play.
The Englishman, who reached the last 16 only once in 14 appearances before the tournament moved to TPC Harding Park this year with a new format which splits the 64 players into 16 groups of four, birdied the last for a one up victory.
That gave Westwood, who won in Indonesia on Sunday, the perfect start to the round-robin format, with Mikko Ilonen up next after the Finn lost his first round-robin game to Masters Tournament champion Jordan Spieth.
“It was a real struggle out there,” said Westwood. “We didn't see a lot of each other on the front nine. It's probably a game that Matt thinks he should have won - I feel very fortunate to win.
“Neither of us played particularly well, but we scrambled a lot and ground it out. Sometimes to win a match play match you have to do that. I guess I birdied three of the last four holes.”
Martin Kaymer recorded a 3 and 1 win over Thongchai Jaidee, and Sergio Garcia was a two up winner over Tommy Fleetwood, but the news was not so good for some of their Ryder Cup team-mates from Gleneagles.
Four members of Europe's Ryder Cup winning side suffered defeats on the opening, but the new format meant they were at least spared an instant exit in San Francisco.
Justin Rose, Ian Poulter, Henrik Stenson and Stephen Gallacher all lost their first group matches.
Rose came into the event on the back of winning the Zurich Classic on Sunday in his first appearance since finishing second in the Masters, but was never in front against Australian Marc Leishman before losing 3 and 2.
Leishman, who withdrew from the Masters as his wife recovered from a life-threatening illness, won the opening hole with a birdie and moved two up when Rose bogeyed the third, the Englishman having played his last 66 holes at TPC Louisiana without a dropped shot.
Rose, who was unbeaten in five matches and Europe's leading points scorer in their victory at Gleneagles last year, twice got back to just one down but a bogey on the 11th was followed by a Leishman birdie on the 12th and there would be no way back for the world number six.
Poulter lost the opening hole to a birdie from former US Open Champion Webb Simpson, but ultimately paid the price for carding four bogeys in six holes from the third as Simpson gained a measure of revenge for losing to the Englishman in the 'Miracle at Medinah' in 2012.
"I've drawn him in the last two Ryder Cups and what a match player he is," Simpson said. "He is always tough and even being three or four up I knew I couldn't let up and I'm happy to get by for sure."
Stenson thought he had halved his match with John Senden when the Australian birdied the 18th, only to be told extra holes would be played to determine the result, Senden securing victory with a birdie on the 19th.
Defending champion Jason Day also lost his opening match 4 and 3 to American Charley Hoffman.
Shot of the day had come from American Ben Martin, who fired a hole-in-one on the 17th to take the lead over Matt Kuchar before sealing victory on the last.
McIlroy was among the later starters and was all square after two holes against former US PGA champion Jason Dufner.
Garcia recovered from two down to beat Fleetwood by two holes in the all-European Group 10, where Jamie Donaldson edged out Austria's Bernd Wiesberger on the 18th.
"He (Fleetwood) played well all day then hit a couple of iffy shots in the last five holes and I was able to take advantage," Garcia said.
Danny Willett enjoyed a successful debut in the event with a 3 and 2 win over Ryan Moore, but in the same group compatriot Andy Sullivan was left to rue several missed chances as he lost 2 and1 to American Ryder Cup star Patrick Reed.
Two-time Masters champion Bubba Watson enjoyed a comfortable 5 and 4 win over Miguel Angel Jimenez, while McIlroy had taken advantage of three bogeys from Dufner to move three ahead at the turn.
