US Open Golf 2013: Contenders to Watch Entering Day 3

As Day 3 of the U.S. Open 2013 gets underway, the contenders at Merion are beginning to come into focus. 

Here's how the leaderboard looks like heading into Day 3:

Which have the best chances of separating themselves from the field?

Billy Horschel

Horschel is playing the best golf of his career at the right time. The 26-year-old hit all 18 greens in Round 2. Despite being an unknown to many, Horschel has been having a terrific year. He won the Zurich Classic, finished tied for second at the Shell Houston Open, tied for third at the Valero Texas Open and tied for ninth at the RBC Heritage. 

After dealing with injuries early in his career, Horschel is finding his stride. Horschel told Sports Illustrated that his game has changed as he's gotten older:

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"I've acquired some patience," Horschel said. "Not as much as I wish I had. But I just think that the older I get, the more mature I get on the golf course, the more I understand that if I do have a bad stretch of holes, I don't hit the panic button right away."

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The biggest question for Horschel is if he can continue this play. And if he does, how will he deal with the pressure? This is the biggest moment of Horschel's career. Was Round 2 a fluke? Was it simply a a case of a good golfer getting lucky?

Or, does Horschel have what it takes to continue this remarkable run?

The start to Day 3 will be a great indicator. If he gets off to a hot start, then the slipper will still fit for this Cinderella story. If he wilts under the pressure, it will be seen early. The more he plays like this, the better chance he has.

Phil Mickelson

Lefty is back. Although he didn't have the best Round 2, Mickelson is still tied for the lead. 

He hit just one birdie, but his 72 for the day was enough to get him under par. He told ESPN he was happy with his performance:

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I played really well. Even though I shot 2 over, it was the birdie opportunities that I didn't capitalize on. Had I made one on 2 or that birdie on 8 or 9 or 11, I would have changed kind of the momentum of the round. I played well today even though I didn't feel the score was what I thought it should be.

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In order to keep up with Horschel, Mickelson will need to start hitting more birdies. His first round helped him survive the only decent second round. But now that the leaderboard is a bit more crowded, Mickelson's putter will need to be more consistent. 

Still, he is crushing his irons, hitting 75 percent of both greens and fairways. That will keep him in it. But the more his putter betrays him, the less of a chance he has of winning.

Luke Donald

Luke Donald had a disappointing second round, but he still in contention. He was a two-over 72, including four consecutive bogeys on the back nine.

His first-round performance, in which he shot two under, gives him a chance. But which golfer will show up for Day 3? Will it be the smooth one that made Merion look easy in the first round? Or the golfer who couldn't find his stroke and let Merion beat him?

The weather certainly had an impact, but with the day setting up to be gorgeous, Donald has a chance to regain his first-round swagger.

He's just one shot back. If his putter can get back into form. For his part, Donald is keeping calm, telling the Telegraph that:

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“You don't panic in the US Open,” he said. “US Opens notoriously get more difficult as the week goes along. The pin positions were difficult and even the short ones were difficult to read. This is a tough course.”

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Look for Donald to put a big third round, and gain a steady hold on the lead.