England have been reduced to 285-7 at tea on day three of the second Ashes Test at Lord's.
The hosts must reach 367 if they want to avoid the follow-on.
With Moeen Ali now alongside him, Cook continued to battle away in the middle with dogged determination. However, his resistance was ended when Mitchell Marsh bowled him four runs short of his century.
Ali (38*) and Stuart Broad (5*) are currently at the crease for the Three Lions.