Phil Mickelson was on fire in his PGA Tour Champions debut Monday firing 11 birdies in a 10-under par 61 at Ozarks National to lead the Charles Schwab Series event. Mickelson made five straight birdies on the back nine to lead Australian David McKenzie by one stroke. The five-time major champion became eligible for the Champions circuit when he turned 50 in June.

“I had a lot of fun,” said Mickelson, who played alongside Retief Goosen and Steve Stricker.

Mickelson birdied that first hole at Ozarks National Golf Course in Ridgedale, Mo. He drove the green on the 345-yard, par-4 3rd hole, almost springing out of his shoes on his swing. Another birdie. He birdied 4, 5 and 7. Three more birdies. He bogeyed 9, but then birdied 11, 13, 14, 15, 16 and 17. Eleven birdies in all.