Phil Mickelson pleased with mental approach after putting himself in contention at the St. Jude Classic

A week before trying to complete the career grand slam at the U.S. Open, Mickelson became ragged off the tee late in his round but avoided too much damage

Mickelson was pleased with his approach at the St. Jude Classic (Getty)

Phil Mickelson gave his focus a thumbs up after carding four-under-par 66 to trail first-round leader Seamus Power by one stroke at the FedEx St. Jude Classic in Tennessee on Thursday.

A week before trying to complete the career grand slam at the U.S. Open, Mickelson became ragged off the tee late in his round but avoided any damage at TPC Southwind in Memphis.

"I finished the round off, even though I didn't quite have it there at the end," Mickelson said. "I had a nice simple round going and then I missed the last four fairways.

"I was able to gather myself well and control my thoughts a little bit better."

Mickelson said after a first round 74 at last week's Memorial that his focus had been lacking but he subsequently gathered himself to tie for 13th.

By playing in Memphis, the 47-year-old is continuing his traditional build-up for the U.S. Open.

A six-times U.S. Open runner-up, he has had three chances since winning the 2013 British Open to become the sixth player to complete a career grand slam, but he has not come close.

He even skipped last year's event - won by Brooks Koepka at Erin Hills - to attend his daughter's high school graduation.

Koepka matched Mickelson's 66 on Thursday, saved by a putter that was almost as hot as the Memphis weather.

"I didn't play well at all," he said. "We were all over the place. I'm a good putter. I just need to figure out everything else."

Mickelson was satisfied after round one (Getty)

World number two Dustin Johnson also started well with a 67 that included a chip-in birdie at the par-four 12th.

After his approach shot ended in a hazard but dry, Johnson removed his right shoe and sock, took his stance in the mud and choked down on his wedge, before knocking the ball into the hole.

"I actually didn't hit it very well and got lucky and it went in the hole," he said modestly.

Leader Power, an Irishman who went to university in Tennessee, capped off his day by hitting his approach shot to five feet for a birdie at the last.