Kei Nishikori recovered from a second-set slip-up to give himself a fighting chance of reaching the last four of the ATP World Tour Finals with victory over Tomas Berdych.
Nishikori and Berdych lost their opening matches to Novak Djokovic and Roger Federer respectively, but it was the eighth seed who emerged victorious in the tightest encounter of this year's tournament so far.
The 2014 US Open finalist triumphed 7-5 3-6 6-3 in two hours and 23 minutes, marking his fourth win in five matches against the Czech.
Berdych saw his serve come under pressure early in the match and was forced to survive two break points to hold serve in the fifth game.
However, having fought back from 15-40 down at 5-5, Berdych surrendered the break by sending a forehand into the net, with Nishikori then sealing the opening set with a searing shot down the line.
Nishikori had seemingly carried his momentum into the second set as he raced 2-0 ahead, only to hand Berdych the break back to level at 2-2 with a double-fault.
Berdych then took command of the set by rattling off the next three games for the loss of just one point and, after Nishikori had stemmed the tide with a hold, served out the set to love to force a decider.
Two break points went begging for Nishikori in the second game of the third, but he held from 30-40 down at 3-3 before Berdych's defences finally wilted as he fell 5-3 behind.
And Nishikori made no mistake in serving out the match, doing so with a somewhat fortunate backhand slice from the baseline that just dropped in.
Nishikori  bt Berdych  7-5 3-6 6-3
Berdych - 5
Nishikori - 4
BREAK POINTS WON
FIRST SERVE PERCENTAGE
Berdych - 50
Nishikori - 59
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Berdych - 69/50
Nishikori - 75/50
Berdych - 94
Nishikori - 99