If the Masters starts on the back nine on Sunday, the U.S. Open at Torrey Pines may well start on the back seven. Through two-plus rounds, the final seven holes present three of the fiercest tests on the course -- Nos. 12, 14 and 15, which have played as the first, fifth and third toughest holes, respectively.   

Here are the five toughest holes overall, and their stroke averages, so far this week:

12th, par 4, 504 yards   (4.61)
6th, par 4, 515 yards    (4.54)
15th, par 4, 478 yards   (4.41)
1st, par 4, 448 yards   (4.373)
14th, par 4, 435 yards   (4.371)