The third round was suspended for the day with four-time major champion Koepka, looking to strike a massive blow for golf's breakaway group, holding a four-shot lead over World No.3 Rahm.

Koepka moved to 13-under-par through six holes, one-under on the round, before officials stopped play at an Augusta National that suffered a constant deluge of rain on Saturday.

“It's obviously super difficult. Ball's not going anywhere. You've got rain to deal with, and it's freezing cold. It doesn't make it easy,” Koepka said after the suspension of play.

“You've got to make some pressure putts. You know it was going to be a difficult day. You've just got to grind through it and try to salvage something.”

Thirty-nine players, including Rahm, had already returned early on Saturday morning to finish off their second rounds.

The Masters committee then applied a split-tee format with threesomes for round three in desperate hope of catching up.

But play eventually had to be abandoned at 3.17pm local time when greens became saturated, leaving players facing a gruelling Sunday schedule at the year's first major championship.

Jon Rahm is Koepka's nearest pursuer with plenty of holes left to make a move. PHOTO: Andrew Redington/Getty Images.

Koepka will return in the box seat after picking up a birdie on the par-5 2nd hole, then making four successive pars as his chasers struggled to keep up in the relentless rain.

Rahm briefly cut the deficit to two strokes until bogeys on 3 and 4 doubled Koepka's advantage.

Fresh off his victory at last week's LIV Golf League Orlando event in Florida, Koepka has gone 29 holes without making a bogey and is looking almost impossible to chase down.

“I'm not too concerned about playing 29 holes or however many holes we've got left,” the American said. “It's part of the deal. I'm pretty sure I'll be up for it considering it is the Masters. So I don't think anybody should have a problem with that.”

But if anyone is capable of running him down, it is Rahm, who has nine holes remaining in his third round.

With five victories in his past dozen worldwide starts, the Spaniard is the heavyweight the PGA Tour needs to fend off Koepka's bid to be the first player from LIV to win a major championship.

“It looks like it's good weather tomorrow. So we're going to have good weather conditions and most likely a soft golf course,” Rahm said.

“A lot of holes. But feeling good, feeling strong, and keep it going.”

“I'm not too concerned about playing 29 holes or however many holes we've got left. It's part of the deal. I'm pretty sure I'll be up for it considering it is the Masters." - Brooks Koepka.

Aside from Rahm, Koepka's next closest pursuer is American amateur Sam Bennett at six-under.

Like Koepka and Rahm, Bennett also has 12 holes of his third round remaining before Sunday's final round which is scheduled to start at 12.30pm local time.

Patrick Cantlay, Collin Morikawa, Matthew Fitzpatrick and Viktor Hovland are all five-under and eight shots adrift of Koepka.

Jason Day is the leading Australian, nine shots off the pace in a five-way tie for eighth at four-under with three-time champion Phil Mickelson, Cameron Young, Justin Rose, Russell Henley and Joaquin Niemann.

World No.1 and defending champion Scottie Scheffler is one stroke further back in a share of 14th with Kiwi Ryan Fox.

Open champion Cameron Smith (one-under) and 2013 Masters winner Adam Scott (even par) both have five holes of their third rounds remaining.

Tiger Woods made a record-equalling 23rd consecutive Masters cut on the number at three-over before falling well back in the third round.

47-year-old Woods battled valiantly, walking the hilly course on his rebuilt leg, to post a steely second-round 73.

But successive double bogeys on the 15th and 16th holes, his 6th and 7th of the day having started from the 10th in his third round, sent the five-time champion crashing to nine-over and last of the 54 players left in the field.

Still, Woods joined Gary Player (1959-82) and Fred Couples (1983-2007) in the record books with the most consecutive Masters cuts made.

At 63, the 1992 champion Couples also penned another piece of Masters history by becoming the oldest man to make the cut at Augusta.