Surrey 193 for 2 (Finch 114*, Roy 50) beat Sussex 176 for 7 ( Nash 53, Batty 4-24) by 17 runs
Australian Aaron Finch revived Surrey's hopes of reaching the knockout stages of the NatWest T20 Blast with a brutal hundred against Sussex at the Kia Oval.
Finch muscled his way to an unbeaten 114 - his third hundred in the format - to help set up victory by 17 runs against Sussex Sharks in front of a crowd of 13,229.
The 30-year-old equalled the Surrey record of seven sixes in a T20 innings held by Mark Ramprakash, striking four of them in a remarkable assault on David Wiese in the 18th over.
Finch cleared the ropes off four successive deliveries - two over midwicket and two over long-off - before hitting the last balls for four in an over which yielded 30 runs and transformed the Surrey innings.
Finch and Jason Roy, whose 50 was his highest score in this season's Blast, had posted 91 in the first ten overs, but Surrey only added 31 in the next five as Chris Jordan, whose four overs cost just 19 runs, and leg-spinner Will Beer (1 for 23) dragged Sussex back into contention.
Then Finch launched his withering assault on Wiese as Surrey plundered 71 off the last five overs to get them to 193 for 2.
Finch finished on 114 off 64 balls with seven fours and seven sixes, the other three struck during the Powerplay. Roy cleared the ropes four times in a 33-ball half-century before holing out to deep mid-wicket.
A target of 194 was always going to be tough to get on a pitch already used twice this summer during the Champions Trophy but Chris Nash kept Sussex's hopes alive with his fifth half-century in this season's Blast.
The opener struck 53 off 38 balls, with five fours and two sixes, but after he was caught on the long-on boundary in the 14th over Sussex's chase fizzled out, although Jordan and Jofra Archer added an unbeaten 39 at the end.
Nash played well without being able to match Finch's power and while he and Stiaan van Zyl were adding 48 in 29 balls for the second wicket Sussex had a chance.
But van Zyl was caught at deep mid-wicket for 29 off Gareth Batty's first ball and it turned into a profitable afternoon for Surrey's captain.
Batty bowled his left-arm spin adroitly on a pitch giving him some assistance to finish with 4 for 24 including the key wickets of Nash, Ross Taylor, whose 11 continued a disappointing run of scores for the Sussex captain, and former Surrey player Laurie Evans (6).
Taylor's side must now beat Essex at Hove on Friday to have any chance of squeezing into the last four while Surrey will probably need to win both their remaining games. Both are among five counties locked on 12 points in the table.