ARDMORE. Heavy rain at this week’s U.S. Open has raised the question of whether mud balls could affect the outcome of the championship.Despite two days of warm, drying weather after more than six inches (15 centimetres) fell on the Merion course, more rain was forecast for Thursday’s opening round.When the ground is so heavy, it is not uncommon for mud to stick to balls hit in the fairway, making it harder to control the next shot.Graeme McDowell, the 2010 U.S. Open winner at Pebble Beach, said the randomness of getting a mud ball could throw the competitive balance off."It is an element of chance as to how your ball pitches in the fairway, does it pitch in the upslope, does it pitch in the downslope, are you a low ball hitter or a high ball hitter, how much mud is your ball going it to pick up,” McDowell said."If it’s a long shot it literally can cost you shots. So it’s unfair.”Three-times U.S. Open champion Tiger Woods was less concerned. "I think there’s an element of luck anytime you win a golf tournament,” Woods said."The good news is that most of these holes that we’re going to have potential mud balls on we’re going to have short irons in. You can get the ball on (the green) a little easier with a short iron.”Steve Stricker, playing in his 18th U.S. Open, said he believed golf balls used by professionals these days were more prone to mud."We’re more apt to get a mud ball nowadays than we were earlier on in my career,” said Stricker. "It seems like (it takes) less mud to affect the ball.