(CNN) -

Two late bogeys left Rory McIlroy a frustrated figure in Colorado but the four-time major winner was hoping a spot of gridiron would help lift his spirits.

The Northern Irishman is still tied for the BMW Championship lead on three-under despite that slump, but his thoughts immediately turned to the Seahawks' NFL clash with the Packers.

McIlroy, who described himself as a "big time" football fan, said: "Even though you guys play with pads on, which ... I don't understand."

The 25-year-old met Denver Broncos quarterback Peyton Manning at Cherry Hills Country Club on Tuesday, who handed over tickets for its opener against the Colts on Sunday.

And McIlroy is well placed to head to Mile High Stadium as the leader of the FedEx playoffs after he joined Americans Gary Woodland and Jordan Spieth at the top of the leaderboard.

The 2014 British Open and U.S. PGA champion had been out in front on five-under but dropped two shots in his final three holes to sink back into the pack.

"I'm a little frustrated coming off the course, because I feel like it should have been better than what I finished," McIlroy told Sky Sports.

"But you can see by the scores, it's pretty tricky out there ... so a 67 is a really good start, even though it could have been a bit better.

"The fairways are firm so even when you're hitting irons and fairway woods off the tees they're running out and through fairways and into the rough and the rough is thick.

"Then the greens are so firm, the greens have got so much firmer over the past 24 hours and it's really made a huge difference."

The course's elevation has suited big hitters like McIlroy, who was launching drives nearly 400 yards in his practice rounds prior to the tournament.

But the different air conditions make it more tricky to judge distance and ball flight, with several players overshooting greens on the opening day.

Added to the firmness of the course, and the punitive rough, McIlroy compared it to a U.S. Open style test.

"I wouldn't say it's quite as difficult as (a U.S. Open), but it's thick rough, especially around the greens, and firm greens," McIlroy added. "That's what they need to keep the scoring the way it is."

Woodland led for a long stretch on the opening day and dropped only one shot during his round, at the 4th, later describing the greens as "concrete."

U.S. Open champion Martin Kaymer, from Germany, is in a group of nine players on two-under that includes Sweden's 2013 FedEx Cup winner Henrik Stenson.

Five-time major winner Phil Mickelson is two shots further back on level par and said the set up in Colorado was reminiscent of one of Amreica's most famous tracks.

"It reminds me of Augusta in the early '90s, when the course played very short and the greens were the defense," Mickelson said.