The defending champion laid waste to Augusta National yesterday as he carded a faultless round of 66 to hold a two-shot cushion on 6-under par.
But Shane Lowry is right on the coat-tails of the world number two.
Lowry holds a share of second place on 4-under par after brilliant round of 68 that leaves him alongside Dany Lee.
Rory McIlroy bogeyed two of his final three holes in the tough scoring conditions last night to sit on 2-under par.
Of the other two Irish players, Graeme McDowell is on level-par while Darren Clarke is facing a tough day when he resumes from 4-over par – the European Ryder Cup captain will be the first Irish player to tee-off once-again today when he returns to the course just before quarter-to-two.