Despite not having played the TPC Four Seasons Resort Las Colinas in practice this week, the Spaniard holed out with a sand wedge to eagle his opening hole on the way to a sparkling four-under-par 66.
Garcia also carded three birdies and a lone bogey at the par-four 15th in dazzling sunshine to end the first round two strokes behind pace-setting American Jeff Overton.
Ryan Palmer, also of the United States, was alone in second after two birdies in his last three holes earned him a 65.
“It was definitely a nice round to start the week,” Garcia, 31, told reporters after finishing the day among a group of nine players on 66.
“On Tuesday I didn’t think I had a chance of playing... the finger was so sore. But we worked on it ... they gave me some antibiotic cream and I kept putting on that cream and taking the antibiotics.
“It definitely feels better. A little sore but definitely I can play without having to think about it, which is good.”
Garcia, who withdrew on Monday from the US qualifying tournament in nearby Plano, Texas, for this year’s British Open, surprised himself with his red-hot start to the round.
He hit a wayward drive on his opening hole, the par-four 10th, but was fortunate to end up with a good lie close to a cart path for his second shot, 115 yards from the flag.
“I thought if I hit a good shot with a sand wedge I could start with a birdie and calm me down after everything that’s been going on through the week,” said Garcia, who won the Byron Nelson Championship in 2004.
“And I hit it and I saw guys on the green saying ‘in’ and I thought: ‘Perfect!’ I couldn’t have started in a better way.”
The former world number two is bidding for his eighth PGA Tour title but his first since the 2008 Players Championship.
Overton, runner-up in last year’s Byron Nelson Championship, took control at the TPC Four Seasons late in the day with a bogey-free 64, his lowest round this season.
In pursuit of his first victory on the US circuit, the 27-year-old hit 11 of 14 fairways and 16 of 18 greens in regulation to surge to the top of the leaderboard.
“It’s nice having confidence because of last year,” Overton said after recording four birdies in his last eight holes. “I was able to hit a lot of great shots and strike out early. I hope this is the beginning of a good streak for me.”
Overton has posted just one top-10 in 13 PGA Tour starts this year, a tie for sixth at the Honda Classic in March.
“I’ve been hitting it really well the last three or four weeks, I just have not made my putts all year,” he said. “Hopefully this is a break-through round and I can carry it over.”
Australian Jason Day did not fare anywhere near as well as Overton as he launched his title defense with a 72.
Winner here by two strokes last year, Day bogeyed three of his first six holes and then fought back to level before double-bogeying the par-four ninth, his final hole, after hitting his second shot into water.