Mickelson closed with a birdie at the last hole of the TPC River Highlands course for a seven-under-par 63 that brought him to 13-under on the week and one shot clear of first-round leader Mackenzie Hughes (68) and sponsor invite Will Gordon (62).

Australian Marc Leishman shot a strong 65 to ensure he sits a further three shots behind on nine-under, along with world No. 1 Rory McIlroy (68), Xander Schauffele (68), Brendan Steele (62) and Brendan Todd (65).

Mickelson, in his first tournament since turning 50 last week, will have a short turnaround as third round action will feature threesomes off split tees starting at 7 am (local time) due to expectations for inclement weather later in the day.

"It's probably a little bit difficult as you get older, but when you're playing well, you have that extra momentum, and it should be okay," said Mickelson.

Denny McCarthy withdrew ahead of his second round after he became the third PGA Tour player to test positive for COVID-19.

"Last night, I woke up in the middle of the night with additional aches and soreness and sensed something was off," said McCarthy.

"I felt like the only thing to do was get tested at that point before I went to the course."

Bud Cauley, who played the first round with McCarthy, tested negative twice but withdrew as a precautionary measure, bringing the number of coronavirus-related withdrawals this week to seven.

Jason Day and Greg Chalmers - both four-under - were the only other Australians to survive the second round cut.

Australian Associated Press