Peter Hanson made a blistering start to the HP Byron Nelson Championship to establish a one-shot lead after the opening round at the TPC Four Seasons Resort.
The Swede missed the Wells Fargo Championship a fortnight ago with a back injury but he showed no signs of any rustiness as he carded a five-under-par 65 in Irving, Texas.
Five of his six birdies came during a brilliant front nine, which saw him turn in 30, and although he could only come back in level par - bogeying the 14th before claiming another birdie on the last - he had done enough to sit atop the leaderboard.
Hanson, playing this course for the first time and looking for his maiden PGA Tour title, said on www.pgatour.com: "Always nice to get off to a fast start.
"I got off to a really good start, had a few chances coming back in and made a bit of clumsy bogey from the fringe on 14, but those things happen."
Ireland's three-time major winner Padraig Harrington will be happy with his opening round as he started with a 68, leaving him well placed.
Hanson's nearest challengers are Marc Leishman, David Duval and Tim Wilkinson, who are all on four under.
Duval almost pulled out prior to the start due to an elbow problem but he was able to last the day and four birdies in his final five holes saw him rocket up the standings.
"I left no stone unturned trying to make sure I got to tee off today and it worked out," said Duval. "I hope I feel fine tomorrow."
One shot further back is Hanson's 2012 Ryder Cup team-mate Martin Kaymer, who is looking to claim back-to-back wins following his victory in the Players Championship on Sunday.
The German, who finished joint fifth on his debut here last year, is one of eight players who shot 67s on Thursday.
Further down the leaderboard world number five Matt Kuchar fired a one-under-par 69, while 20-year-old home favourite Jordan Spieth, who finished tied for second at the Masters, carded a 70.