CNN  — 

He turned 50 in June and has experienced nearly everything there is to experience in golf but after making his PGA Tour Champions debut and shooting an impressive first-round 61, Phil Mickelson admits he still gets nervous before he plays.

“I was a little nervous because I wanted to come out and play well,” Mickelson said afterwards. “I felt like I was playing really well … I’ve been playing really well at home and I get out on Tour and I’m playing tight, not letting myself go and swing free and aggressively.

“I get a little steery. To come out here and compete, it gives me a chance to work on that.”

The five-time major winner didn’t let any nerves show though, birding the first hole at the Ozarks National Golf Course in Missouri on the way to a 10-under par 61 to lead the Charles Schwab Series event.

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Mickelson hits from the 18th fairway during round one of the Charles Schwab Series.

Mickelson finished with 11 birdies in his opening round to lead David McKenzie by one stroke. He became eligible to compete on the Champions tour when he turned 50 in June.

He had said earlier this season he didn’t expect to compete on the Champions Tour and instead preferred to focus on the PGA Tour. But having missed the cut at the Northern Trust at TPC Boston on Friday and having been eliminated from the FedEx Cup Playoffs, he chose to take part for the first time.

“I had a lot of fun,” said Mickelson, who was in the same group as two-time US Open winner Retief Goosen and Steve Stricker.

“I enjoyed competing against Retief for so many years and Steve Stricker is one of my favorite people in all of golf. Watching Stricker roll in putts early in the round gets your mindset in a very positive frame and I tried to kind of take his feel and touch and rhythm of stroke and I made some on the back.”

Mickelson lines up a putt on the 13th green during round one of the Charles Schwab Series.

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Mickelson is still eligible to play in PGA Tour events despite now competing on Champions tour.

Only 19 players have won in their first start on the PGA Tour Champions, most recently Jim Furyk.

And given how well known he is, Mickelson knew that his debut would have garner interest and he felt the pressure to perform.

“The expectation is there,” he said. “If you play well and win, well, you’re supposed to do that. If you don’t, it’s like, what happened? I wanted to make sure I was playing well when I played in my first one.”