Thomas beat Will Zalatoris in a play-off at last year's PGA Championship and if he wins again this weekend, he will become only the third golfer in the last 80 years to win consecutive titles.

But Thomas, who was seven shots down after 54 holes at last year’s event, is tied at odds of 20-1 along with Dustin Johnson and Jason Day.

Spain's Jon Rahm, whose Masters win returned him to the world number one spot in the rankings, is joint-favourite with world number two Scottie Scheffler at 7-1, Northern Ireland’s Rory McIlroy at 11-1 and with Patrick Cantlay and Brooks Koepka at 18-1.

Zatoris is absent because of a back injury, but 99 of the top-ranked players will be involved.

One big-name absentee is four-time winner Tiger Woods, who is recovering from ankle surgery after he withdrew during the third round at the Masters.

McIlroy, 34, is a 23-times PGA Tour winner and won this event in 2012 and 2014.

However he hasn't won a major in his last 29 attempts and has missed the cut in two of his last three tournaments after struggling with his putting.

Xander Schauffele, who won Tokyo 2020 Olympic title, is a favoured outsider for the title at 22-1.

He has achieved five successive top-10 finishes on the PGA Tour.

His predecessor as Olympic champion Justin Rose of Britain, who won at the Rio 2016 Games, is also in a field of 156 players which does not include a single amateur.

This will be the fourth time that Oak Hill is staging the PGA Championship with previous winners on this tricky par-70 course being Jack Nicklaus in 1980, Shaun Micheel in 2003 and Jason Dufner in 2013.

The course was almost entirely remodelled in 2019 but accuracy off the tee remains important with deep fairway bunkers and thick rough lying in wait for stray drives.