Those players occupy the top five spots in the World Golf Rankings.
But the 2013 British Open has not played out according to form. Here are the top surprises in the opening two rounds of this classic major tournament.
Miguel Angel Jimenez of Spain may not win the British Open even though he has the lead at the halfway point, but he is not going to be intimidated by his surroundings or his competition.
Jimenez is not an every-week competitor on the PGA or European Tour, but when he plays, he's regularly a factor.
Jimenez is not a pure athlete—he often does his warm-up exercises with a cigar in his mouth—but he does have a classic golf swing that often delivers pure results.
The Spaniard is not going to go away, and it will take a substantial effort to beat him.
Brandt Snedeker has all the tools needed to contend in the major tournaments on a consistent basis.
His game would seem especially well suited for the British Open because of his versatility and shot-making ability. However, he has never won a major, and the best he has done is tie for third in the 2008 Masters and the 2012 British Open.
After an opening round of 68, Snedeker appeared to be in a terrific position to launch his assault at Muirfield. However, he had a disastrous second round in which he had three double bogeys and a triple bogey.
Snedeker shot a 79 and will need two excellent rounds on Saturday and Sunday to have a chance to get close to the leaders.
When it's a big tournament, Angel Cabrera will make his presence felt more often than not.
Even though he's the 53rd-ranked player in the world, Cabrera finds himself two strokes off the lead at the Open Championship. Cabrera seems to be completely devoid of nerves.
Cabrera followed an opening round of 69 with a 72 on Friday, and that left him in a good position to make a run at the championship over the weekend.
Cabrera played brilliantly in the Masters before losing in a playoff to Adam Scott. Perhaps he'll make up for that close-but-no-cigar finish at Muirfield.
One thing golf fans know about Phil Mickelson is that at one point or another, he is going to get that eagle-eyed look and attempt a shot that 99 percent of his competitors would never even consider.
Having the guts to try dangerous shots is part of Mickelson's signature. It has won him tournaments, and it has lost them for him.
After shooting a 69 in the opening round, Mickelson put the gambling part of his persona on hold in the second round. He double-bogeyed on the second hole, and that's normally the kind of score that triggers a more aggressive game from Mickelson.
Not this time. He tried to steady himself the rest of the round, and he never tried to go beyond the norm. He played one-under-par golf from Hole 3 through Hole 15, making three birdies and two bogeys. He made another double on 16, but he recovered with a par on 17.
Mickelson is plus-one for the tournament, but he is just four strokes out of the lead, and he remains a prime contender.
There's no doubt that Rory McIlroy has been struggling all season. He may have been the No. 1 player in 2012, but 2013 has been a struggle all the way through.
Even with all of his troubles, McIlroy was still a factor coming into the British Open. Perhaps not to win, but at least to be a possible contender.
Instead, McIlroy played poorly at Muirfield. He shot 79-75 for a 12-over-par 154, and he didn't come close to making the cut. Instead of competing for four rounds, he will be a mere spectator for the weekend.
McIlroy is no longer in a mini-slump. He is in a full-fledged funk, and he has a lot of work to do to get out of it.
On a day when the wind and the challenging course conditions frustrated most players, Englishman Lee Westwood played himself into contention with a sensational second round.
Westwood shot a 68, and he is just one stroke off the lead heading into the weekend. However, what was most surprising about his play on Day 2 of the British Open was his scintillating 31 on the front nine.
Westwood was actually six under through the first 12 holes, but he closed by going three over par on the final six holes.
Westwood will be one of the crowd favorites in the final two rounds.
Zach Johnson was looking confident and serene after the first round of the Open Championship when he shot a five-under-par 66.
However, even though he performed with a certain crispness on Day 1, he had none of that going for him on Friday. Instead of attacking, he was done in by the wind and the unforgiving Muirfield hard terrain. He shot a 75, and that four-over-par round left him one under heading into the weekend.
Johnson is still in a good position, as he is just two strokes off the lead. However, he wore the expression of a man who saw it all slipping away, and he's got to change that before he competes on the weekend.