Rory McIlroy had to dig deep on his debut as Spain's Jon Rahm lit up the Farmers Insurance Open with a blistering 10-under 62 at Torrey Pines.

As the Northern Ireland star chiselled out a workmanlike one-under 71 on the testing,  7,698-yard  South Course, 2017 champion Rahm (24) ripped up the more benign North Course, making the first of two eagles and seven birdies to match the lowest round of his PGA Tour career.

“It's actually the first time I played the North course first,” said Rahm, who was out in seven-under 31 before following his only dropped shot of the day at the third with four birdies in a row from the fifth.

“Usually when you go South the first day, you're kind of trying to survive and trying to post a score. So when you tee off on that course, you know you have to shoot under par to keep up with the average.

“That was the mentality, but when I started the way I started, right, I started with an eagle, made a chip-in a couple holes later, 3-under par and hitting good shots, there was no reason to slow down. I just kept the pedal going and got through the rough stretch of the golf course, which is 2, 3 and 4, and was able to finish on a good note."

He led by a shot in the clubhouse from world number one Justin Rose, who was bogey free, and Web.com Tour graduate Doug Ghim, who posted nine-under 63s as Jordan Spieth carded a 65 for his best score for since he shot 64 in the third round of the Northern Trust five months ago.

Eleven of the 14 players to shoot 66 or better played the North Course. Scores

But it was a grind for McIlroy and hard work at times for Tiger Woods, who opened his 2019 account with a two-under at the venue where he has won eight times.

The Co Down man drove the ball very well but made just one birdie going out, holing a 10 footer for an excellent three at the fifth.

But he failed to take advantage of the par-fives, missing from 10 feet after a heavy-handed chip at the sixth before lipping out cruelly at the ninth, where his six footer did a 360 and stayed up.

A poor pitch from the rough short at the 598-yard 13th forced to settle for another five but while he bogeyed the 225-yard 16th after failing to get up and down from greenside sand, he successfully splashed out to four feet at the 18th to finish with a birdie and a 71 that left him tied 74th.

Woods showed some signs of ring rust in his first official start since his Tour Championship win last year, hitting just half the fairways and yet still managing five birdies against three bogeys to end the day tied for 53rd.

It as his first sub-par opening-round at Farmers Insurance Open since he shot 68 in 2013 and went on to claim the most recent of his eight wins at Torrey Pines

“I think I probably could have shot something around 68 or 67 today pretty easily,” Woods said at the South Course, where Brendon Hagy, Chris Stroud and Charles Howell III were the best performers with six-under 66’s. “I hit a lot of good putts that were around the hole that just didn't quite fall in.

“Overall, shooting a couple under par on the South course is not so bad, but now I'm forced to have to shoot a low one tomorrow just like most of the field did over there today. I'm sure the average score over there has got to be close to under 68 today. I've got to go do it tomorrow.”

As it turned out, the field averaged 69.397 on the North compared to 71.628 on the South Course.

McIlroy might have broken 70 had the putter been even lukewarm on notoriously tricky poa greens. He led the field in strokes gained from the tee but while he tidied up nicely inside six feet, he missed everything between 10 and 20 feet and lost nearly a stoke to the field with the blade.

If he drives the ball as well on the North Course today, he will expect to go low if the putter behaves.

The cut should not be a worry for McIlroy but it’s a reality for Seamus Power, however, who opened with a four-over 76 on the easier North Course and faces his sixth missed cut in a row and his seventh in eight starts since the season began in October.

He now needs a sensational second round at the testing, 7,698-yard  South Course today after mixing three birdies with seven bogeys — six of those dropped shots coming in a nine-hole stretch mid-round — after another frustrating day from tee to green, hitting just half the fairways and greens in a 30-putt round.

There was better news for the Irish on the European Tour, as Shane Lowry opened with a three-under 69 in the Omega Dubai Desert Classic.

Live scoring

After brilliantly breaking his three-and-a-half year victory drought in last week's Abu Dhabi HSBC Championship, the Offaly man hit the mental reset button and came up trumps with his first sub-70 round at the Emirates Golf Club since 2012.

He trailed Matthew Fitzpatrick by just four strokes, rifling his approach to just 12 inches at the tricky, 463-yard ninth to end the day tied for 31st.

"I am usually in America at his time of year so a change this year is nice," added Lowry, who got to four-under after 13 holes and then followed back to back bogeys at the fifth and sixth with two closing birdies.

"It obviously did me a world of good last week, and maybe I can continue on and do something good this week as well."

Greystones' Paul Dunne, who missed the cut in Abu Dhabi, finished with two bogeys for a two-under 70 that left him tied for 44th.

Fitzpatrick birdied five in his final six holes en route to a seven-under 65 and a one-stroke lead over an eight-man group that included 2017 Masters champion Sergio Garcia and world number five Bryson DeChambeau.

Meanwhile, Belfast's Damian Mooney is the best of the Irish heading into the final round at the First Stage of the Staysure Tour Qualifying School in Portugal. Scores

His level par 72 left him tied ninth, five shots behind American John Inman and inside the top 20 who will go on to join the likes of Headfort's Brendan McGovern at next week's Final Stage battle for just five cards.

Royal Curragh's Gerry Burke was tied 15th after a 74 with Ballybunion amateur Peter Sheehan tied 22nd after a 75, Kilkenny's Jimmy Bolger joint 31st with 76 and County Sligo amateur Shane Underwood tied 35th after a five-over 77. 

American Ernest Kocs was the pacesetter with a four-under 66 at the other qualifying venue, Silves Golf.