Two years after believing his career was over, Tiger Woods is in contention for a first major title since 2008 in the 83rd Masters, although joint-leader Brooks Koepka poses a sizeable obstacle to one of sport's greatest ever comebacks.

Woods needed a nerve block simply to attend the Champions Dinner at Augusta National in 2017 and flew to London the same evening to consult a specialist about his ongoing back problems.

"I was done at that particular time," Woods said when accepting an award from the Golf Writers Association of America in Augusta on Tuesday. "I had to get a nerve block just to be able to walk and come to the dinner.

"It was tough and uncomfortable. I ended up going to England that night, saw a specialist there, [and] they recommended unfortunately for me the only way to get rid of the pain I was living in was to have the spinal fusion surgery."

The operation was a last roll of the dice but proved a success, Woods returning to competition in November that year and then playing a full season in 2018, culminating in his 80th PGA Tour in the Tour Championship in Atlanta.

Woods also contended for the last two majors of the year and carried on where he left off at Augusta, carding an opening 70 to lie four shots off the lead shared by Koepka, who is seeking an amazing fourth major title in his last seven appearances, and Bryson DeChambeau.

"I thought I hit a lot of good shots and if I missed I missed in the correct spots and had some of the simpler up and downs because of that," Woods said. "I missed a few (putts) for sure, misread a couple and hit one bad one at six but other than that a good solid day.

"The whole idea is to try and peak for four times a year. And so I feel like my body's good and my game's good, it's sharp, so just got to go out there and execute."

Woods had quietly reached the 14th hole in two under par before a wayward tee shot set up a moment of magic from the former world number one, who threaded his second shot through a gap high up in the pines and holed from from 25 feet for an unlikely birdie.

Just one off the lead when he signed his card, Woods then saw the later starters defy a freshening breeze to produce a raft of good scores, Koepka making five birdies in six holes from the 10th and DeChambeau picking up shots on the last four holes.

Phil Mickelson, who would be the oldest major winner in history if he claims a fourth green jacket at the age of 48, also birdied five of the last seven to lie one shot off the lead, with Ian Poulter and Dustin Johnson a shot further back.

Poulter said: "I saw a stat that says at 43 there's a three per cent chance to get the jacket so I have nothing to lose. I can freewheel.

"I came here two weeks ago and played with Lou Holtz (former University of Notre Dame football coach) and he gave me a pep talk, telling me I could win around here if I just did this, this and this. It was a great day."

Woods shot 70 in the first round of each of his first three Masters victories and since lying 33rd after an opening 74 in his 2005 triumph, the last 13 champions were all inside the top 10 after the opening round.

That was bad news for Rory McIlroy, who needs to win the Masters to complete a career grand slam but was joint 44th after an opening 73.

McIlroy was two over par for the day after bogeys on the 10th and 11th but rallied superbly to birdie the 13th, 15th and 16th, only to drop shots on the last two holes.

Defending champion Patrick Reed also shot 73 while world number one Justin Rose and 2015 champion Jordan Spieth both struggled to rounds of 75.