Jason Day has left his World Golf Championships Match Play Championship title defence partly in the hands of others after losing 4 and 3 to Charley Hoffman.

The world No.7 failed to fire against the 56th-seeded American in his opening match at TPC Harding Park in San Francisco, putting his chances of making the round of 16 in serious doubt.

While the new round-robin format means Day hasn’t been sent packing like he would have in the past, he now must win his remaining group matches against Branden Grace and Zach Johnson in the next two days if he’s to advance.

He must then hope Hoffman slips up in his remaining two matches or Grace remains winless.

If Johnson joins Day and Hoffman with a 2-1 record, it would trigger a three-way sudden death playoff on Friday afternoon.

If both Hoffman and Day finish 2-1 alone at the top of the pool, Hoffman would advance on their head-to-head result.

“Obviously I need to go out there and win the next two and whatever happens, happens,” Day said.

“If I sneak through, I sneak through. If not, then it’s my own fault for losing.”

Day was reluctant to offer up excuses, but conceded lethargy, after a rain-affected Sunday in New Orleans last week where he had to play 33 holes, may have put him behind the eight ball.

“No one’s a favourite here in formats like this,” he said.

“It doesn’t matter who you’re playing, you can’t underestimate what they’re playing like leading up to the event, because they may be playing terrible and strike a match here and they play great.

“My preparation wasn’t as solid as it would be normally. I was exhausted. But with that said, I can’t blame being underprepared, if I go out and play terrible golf.