Shane Lowry admitted he had 'nothing to lose' during his first round encounter with world No 1 Rory McIlroy at the WGC Accenture Match Play Championship in Arizona.
The 25-year-old from Clara in Ireland beat his high-flying friend from Ulster by a single hole, after recovering from two down early in the round.
Lowry, who posted three bogeys in his opening four holes, covered the final 11 in four-under at Dove Mountain to reach the last 32 at the expense of last year's runner-up.
World No 68 Lowry, who won five out of eight holes from the sixth, said: "It was much easier for me to play against Rory than it would have been playing against Tiger (Woods), purely because I just know Rory so well.
"It was quite easy that way, but still quite nerve-wracking on the first tee."
Despite their friendship, there was little small talk as the match progressed.
Lowry added: "There wasn't that much chatter and I tried to keep it that way. I said to my caddie, walking down 11 or 12, 'He's not liking this one bit.'
"He's the one under pressure, I've got nothing to lose, so let's have a go from here."
The beaten McIlroy went on: "We were kind of chatting the first few holes and then it was getting pretty tight around the turn, and on the back nine there wasn't much talk out there.
"Shane had a nice little stretch around part of the back nine. I hung in there, but I just didn't do enough. I didn't make enough birdies in the end."