Jon Rahm, forced to withdraw from his last start with a sizeable lead because of a positive COVID-19 test, is a favourite at this week"s U.S. Open at Torrey Pines in San Diego where hometown boy Phil Mickelson seeks the one major that has eluded him. Rahm was running away with the Memorial Tournament -- leading by six shots after 54 holes -- before having to withdraw and go into self-isolation but said on Saturday he was cleared to play after two negative tests in a 24-hour span. The Spanish world number three, in search of his first major, will be in comfortable surroundings on the South Course as he has four top-10 finishes in five events played there, including a win in the 2017 Farmers Insurance Open. "Everybody knows what happened to him with a six-shot lead and the unpleasant thing of COVID, and then having to pull out of that," NBC Sports play-by-play commentator Dan Hicks said on a conference call. "But he"s had great success there, so that"s another story that I think is brewing as he goes out for his first major." A number of big names like world number two Justin Thomas and four-times major winner Rory McIlroy are among those in the 156-player field who will try to snap out of a form slump on a notoriously difficult layout with penalising rough. World number one Dustin Johnson, who missed the cut at this year"s Masters and PGA Championship, has previously said his game is close. "It"s frustrating ... I feel like a lot of it just has to do with I just haven"t putted very well," Johnson said last week before going on to finish in a share of 10th place in his U.S. Open tune-up. "That"s kind of been the trend or the reason why I"ve just been struggling a little bit is more just with the putting." Defending champion Bryson DeChambeau, who overpowered Winged Foot last year to win his first major by six strokes, comes into the year"s third major having finished in a share of 18th place at the Memorial Tournament. DeChambeau was unbothered by Winged Foot"s narrow fairways as he pounded the layout into submission with his driver and then muscled the ball onto the greens from the thick rough, a strategy the world number five could lean on again this week. CONFIDENT MICKELSON Six-times runner-up Phil Mickelson missed the cut at last year"s U.S. Open but arrives this year brimming with confidence after winning last month"s PGA Championship where he became the oldest major winner at the age of 50. For Mickelson, a three-time winner of the PGA Tour event at Torrey Pines, the course he grew up on, this week offers him an incredible chance to become only the sixth person to complete the career Grand Slam of golf"s four majors. "I wouldn"t ever rule Phil out. I never have," former PGA champion Paul Azinger said on an NBC Sports media call. "I can"t rule him out until he quits working at it and from what we observe every week, Mickelson"s out there and he spends as much time practicing as anybody." Brooks Koepka, who counts two U.S. Open wins among his four major victories, may not be at 100% after surgery in March to repair a dislocated kneecap but has proven he can play through pain as he finished runner-up at the PGA Championship. Koepka missed the cut last week in his only U.S. Open tune-up. "That"s probably where I think some of the poor scoring comes from, just from lack of focus," said Koepka. "But as far as commitment to the shot, striking it well, doing what I want with the ball, flighting it, I"m pretty pleased."