Jordan Spieth breathed new life into his bid to complete the career grand slam as Rory McIlroy staged a superb fightback from an "horrendous" start to make the halfway cut in the US PGA Championship.

Spieth needs to win the US PGA to join Gene Sarazen, Ben Hogan, Gary Player, Jack Nicklaus and Tiger Woods in winning all four major titles, but was rated a 50-1 outsider to achieve the feat this week at Bethpage after enduring a poor season.

However, the former world number one added a second round of 66 to his opening 69 to set the early clubhouse target on five under par, a shot ahead of world number one Dustin Johnson and compatriot Daniel Berger.

Berger also recorded a 66 and Johnson shot 67, but the round of the day so far had come from England's Matt Fitzpatrick, whose 65 was a 10-shot improvement on his opening round and left him level par overall.

"I feel like the tougher courses suit my game a little bit more," Fitzpatrick said. "You can't get away with anything 40 yards offline. I think the furthest offline I've hit this week is 10 yards from the edge of the fairway. I've hit a lot of fairways so this has been the key."

McIlroy could certainly not say the same as he limped to the turn in 40 after starting his round double bogey, bogey, double bogey, but the four-time major winner produced a hat-trick of birdies from the fourth and picked up another shot on the eighth.

The resulting 71 left McIlroy on the early projected cut of three over and with the wind forecast to pick for the later starters, almost certainly safely through to the weekend.

"I just needed to see one putt to go in, to see something hit the bottom of the hole and that was on the fourth," McIlroy said. "From there I started to play some good golf.

"I had a horrendous start, five over after three, but came back well and the goal after those three holes was to be here for the weekend and it looks like I have done that, which is nice."

Spieth was second in the world after winning the third leg of the grand slam in the 2017 Open Championship but has not tasted victory since and is currently ranked 39th after failing to register a single top-20 finish this season.

The 25-year-old admitted at the start of the week he was "in a bit of a slump" but carded six birdies and two bogeys to start a major with two rounds in the 60s for the fourth time. He won the other three.

Defending champion Brooks Koepka began his second round on seven under and was among the later starters in a group containing Masters champion Tiger Woods and Open champion Francesco Molinari, who were both nine off the pace after opening rounds of 72.