World No 15, Patrick Cantlay, who won The Memorial Tournament held at Muirfiled Village in 2019, cam back strong on Friday, with a round of 69 on Thursday and 67 on Friday for a score of 8 under.
Cantlay carded a first-round 69 before birdieing the final three holes of his second round to close a five-under 67 and take him to eight under, only for late starter Jon Rahm to move alongside him by playing his opening 13 holes in five under.
The three-time PGA Tour winner ended a run of pars by making a birdie at the seventh and picked up further shots over his closing two holes to grab a two-stroke advantage over Scottie Scheffler, his nearest challenger to have completed 36 holes, with Carlos Ortiz a further shot back after rounds of 71 and 68.
“I’m pretty tired,” Cantlay admitted. “I woke up at 4:30 this morning, started my warm-up, played 33 and this golf course is one of the harder walks, so, yeah, it was a pleasant surprise to birdie the last three!”
Meawhile, Jon Rahm also got to eight under for the tournament with a four under round two so far.
Rahm had five holes to play when darkness saw play suspended at 8.45pm local time (1.45am BST), with the defending champion one of 44 players having to come back on Saturday morning to finish their second rounds.
Rahm started his charge by following a 20-foot birdie at the fourth by getting up and down from a greenside bunker to take advantage of the par-five next, with the world No 3 rolling in a 15-footer at the sixth and making a two-putt gain at the seventh to get within one of Cantlay.
The Spaniard recovered from bogeying the 10th to hole from close range at the next and fired his approach at the 13th to tap-in range to finish his day with a birdie, with Rahm having a chance to claim the outright 36-hole lead when he concludes his round from 8am on Saturday morning.
