By shooting 20-under over the final three founds, American Jordan Spieth took down the John Deere Classic and further secured his standing as the heavy favorite heading into the British Open Thursday. The 21-year-old held par on the first round at TPC Deere Run, and proceeded to fire off 18 birdies and three eagles before claiming his fourth victory of the year in a two-hole playoff Sunday.

Now Spieth’s odds have shifted slightly, from 9/2 to 5/1, as the tour turns to St. Andrews in Scotland and Spieth eyes his third major championship of the year.

"To be able to shoot 20-under in three rounds is nice momentum," Spieth told reporters after besting Tom Gillis in the playoff Sunday. "The finish, when I really didn't feel like tee to green I had much, gives me a lot of momentum to draw on if I don't have my best stuff.”

Since taking down the Masters and U.S. Open in record fashion, and the injury to No. 1 Rory McIlroy, Spieth’s held tight to his favorite status as he lines up golf’s first Grand Slam in the Masters Era. Odds makers must be influenced by Spieth’s impact on history, becoming the first player since Tiger Woods in 2000 to win four tournaments before the trip to St. Andrew’s.

Turning to Spieth’s main competition, neither Dustin Johnson nor Rickie Fowler took on the John Deere Classic, but both saw their Open odds improve. Johnson, 31, has sat behind Spieth and McIlory ever since his crushing runner-up finish at Chambers Bay, but his odds made a small jump from 12/1 to now 11/1. Johnson may have the experience edge over Spieth, finishing tied for second at the Open in 2011.

Fowler missed the cut at the U.S., but took the Scottish Open with three birdies on the final four holes to finish at 12-under over the weekend, and he’s gone from 25/1 to 16/1.

Fowler managed to leapfrog such veterans as Justin Rose (18/1), Adam Scott (20/1), Henrik Stension (20/1), and Louis Oosthuizen (22/1), with Woods moving back from 20/1 to 25/1.

Woods’ slide may have to do with his recent comments about conditions at St. Andrews. He told ESPN and USA Today that he was surprised at how slow the course felt when he returned over the weekend.

"I was shocked," Woods said. "I had seen photos of it a month ago. It was bone dry. It looked like it was going to be one of those dust bowls again; hard, fast, like the years I've played St. Andrews. It's changed. They got big rain and a lot of sun. It's totally changed.

"I'm going to have to do a little bit of feel around the greens, my putting. I wasn't expecting the firmness to be that soft. We made ball marks on the greens. I don't ever remember making ball marks around this place."

Odds to Win the British Open

Jordan Spieth 5/1

Dustin Johnson 11/1

Rickie Fowler 16/1

Justin Rose 18/1

Adam Scott 20/1

Henrik Stenson 20/1

Louis Oosthuizen 22/1

Tiger Woods 25/1

Jason Day 28/1

Bubba Watson 33/1

Hideki Matsuyama 33/1

Paul Casey 33/1

Phil Mickelson 33/1

Sergio Garcia 33/1

Martin Kaymer 35/1

Shane Lowry 35/1

Branden Grace 40/1

Brandt Snedeker 40/1

The full list of odds can be viewed at