Gary Anderson's defence of the World Darts Championship came under a stern examination in a thrilling contest with Dave Chisnall.
Anderson is chasing a third successive crown at the Alexandra Palace but was tested in a 5-3 win which sent him through to the semi-finals.
It was a 180-fest as the pair threw 33 maximums between them, one short of the record in the history of televised games.
Things looked good for Anderson when he checked out on 104 to claim the first set against the throw before holding to take a 2-0 lead.
Chisnall fought back to 2-2 before another sizeable finish - a 124 checkout on the bull - from Anderson restored his lead only for his opponent to respond again.
With both players averaging well over 100, Chisnall was on a roll and found himself in a great position to go 4-3 up but he crucially missed four doubles and Anderson stole the set.
He then ran away with the final set to tee up a last-four date with Peter Wright.
Wright edged out James Wade 5-3 in the afternoon's other quarter-final.
It was another keenly-contested game as Wright was one arrow away from landing the first nine-darter of the tournament while Wade won one set with checkouts of 144 and 155.
Wright assumed control with back-to-back sets and he saw it out.