One of the great things about the U.S. Open is the ability to produce unexpected champions.

Sure, Tiger Woods and Retief Goosen and Jim Furyk and Ernie Els have won the U.S. Open and it's no surprise to see their names engraved on the championship trophy. Each one is a great player and unquestionably a future member of the World Golf Hall of Fame.

But big names and favorites don't have the market cornered when it comes to winning the U.S. Open. Look no further than 2009, when Lucas Glover beat the bad weather, the stops and starts, and produced a clutch final-round performance that was good enough to give him a two-shot victory and his first major title.

Much had been expected of Glover since he arrived on the PGA TOUR from Clemson University, but until that week at Bethpage, he had produced only one victory. Coming into the U.S. Open, Glover was ranked No. 71 in the Official World Golf Rankings. He was 20 spots in the rankings behind Gonzalo Fernandez-Castano of Spain. After his victory at the Open, Glover jumped all the way to No. 18 in the rankings.

Given the possibilities of unexpected winners (remember how Rocco Mediate almost took down Tiger Woods in 2008 at Torrey Pines), here are six players outside the top 50 rankings who might be worth watching this week at Pebble Beach. Each of these guys has the potential to pull a "Glover" and win the U.S. Open.

— Ricky Barnes: One of the three runners-up a year ago, Barnes starts from an almost Glover-like spot (75th) in the rankings. The former U.S. Amateur champion is starting to live up to the high expectations placed on him. He's in the midst of his best year as a professional. He's finished in the top 10 in five high-class events this year: the Memorial, the Verizon Heritage, the Crowne Plaza Invitational at Colonial, the Northern Trust Open and the Masters. Barnes is confident and has been tested. It wouldn't be a surprise to see him respond with a championship effort at Pebble Beach.

— Bo Van Pelt: Hard to believe, but this will be only the fourth appearance in the U.S. Open for Van Pelt, who has been playing professionally since 1998. Van Pelt, who last year won for the first time on the PGA TOUR, has continued to grow in confidence and production. He's lowered his ranking to No. 52, two spots away from Exemption City, and has five top-10s in 2010. He's played well on the tough tracks this year, too: tied for third at Harbor Town and Muirfield Village, tied for fourth at THE PLAYERS, fifth at Quail Hollow and tied for 10th at Colonial.

— Ryan Moore: Having won on the PGA TOUR, Moore's ranking (No. 53) is better than Barnes', even though he's born similar pressures. Moore is the former U.S. Amateur and U.S. Amateur Public Links champion who had his progress slowed by a hand injury that required surgery in his first full season as a professional. Moore tied for 10th at Bethpage, his best showing in four U.S. Open starts. Moore's best showing this season was a tie for fifth at the Memorial.

— Heath Slocum: It seems like Slocum's name is on the leaderboard every week. He's lurking and waiting to take advantage of his chance. He's not yet won a major, but Slocum won The Barclays, the PGA TOUR's first FedEx Cup playoff event, a year ago in dramatic fashion, so he's shown the ability to handle pressure. He tied for ninth at the 2008 Open at Torrey Pines, the only time he's made the cut in three previous starts in the tournament.

— Jason Dufner: He's ranked No. 84 and is more of a longshot, but Dufner's game is suited to making the string of pars required to contend at the U.S. Open. From fairway to green he's quite solid; he ranks 38th on TOUR in driving accuracy and ranks a better-than-average 67th in greens in regulation. If that combination holds at Pebble Beach, the former Auburn University star could be this year's stunner.

— Justin Leonard: Given the grind-it-out nature of his game, it's a wonder that Leonard has never seriously contended at the U.S. Open. Leonard, currently ranked No. 93, has never posted a top-10 in 15 previous U.S. Open appearances. His best was a tie for 12th at Bethpage in 2002. He's missed the cut in three of the last four Opens and at age 38 may be running out of chances.

Things worked out pretty well for Glover. After his U.S. Open victory, he got a chance to lead the Clemson football team down the tunnel and onto the field against Florida State in a nationally televised game. He's now fourth on the points list for the U.S. Ryder Cup team. His World Golf Ranking is No. 21. And nothing he accomplishes for the rest of his career will surprise anyone.

--By Stan Awtrey, PGATOUR.com Contributor