Tiger Woods faces a battle to beat the cut after he endured a difficult time in his first round on the PGA Tour for almost 18 months.

The former world number one, who has been plagued by back injuries, fell apart on the back nine to card a four-over-par 76 at the Farmers Insurance Open in San Diego.

Playing the more demanding of the two courses being used at Torrey Pines, the South, Woods was one over par at the turn and things were looking up when he birdied 10 and 11.

But things quickly unravelled as he bogeyed the next three holes, followed it up with a double bogey at 15 and then went one over again on 17. He did at least finish with a birdie on 18, but he has it all to do on Friday if his return is going to be extended to the weekend.

Woods has undergone two back operations since his last regular tour appearance in August 2015. After a long lay-off he finally returned to tournament play at last month's Hero World Challenge in the Bahamas but his rustiness was evident.

Olympic champion Justin Rose is the first-round leader on seven under.

Playing on the North, he sank two eagles, two birdies and a bogey in his last five holes to card a 65.

He heads to the South Course on Friday in good shape and knows he had to make his opening round count.

He said on Sky Sports 4: "I have been practising well at home. It was nice to get off to a good start and show my range practice pull through.

"It can be a tricky week. The South Course is really tough and if you don't go low on the North Course you are going to feel like you're behind.

"I have been making some putts and I drove the ball really well, especially on the key holes, the par fives."

He is one shot clear of Canada's Adam Hadwin, while Gary Woodland Brad Fritsch, Charles Howell III, Beau Hossler and Trey Mullinax are all a shot further back on five under.