Hampshire 220 for 7 (Ervine 65*) beat Surrey 219 for 9 (Ansari 62) by three wickets
Sean Ervine guided holders Hampshire an important step nearer a place in the Yorkshire Bank 40 semi-finals with an unbeaten 65 as Surrey were beaten by three wickets with eight balls to spare at the Ageas Bowl.
Hampshire still have two Group B matches left in which to be sure of contesting the last four of the competition but they had to overcome a shaky start before finally defeating Surrey's brave challenge.
The two teams meet again in the semi-finals of the Friends Life t20 at Edgbaston on Saturday with Hampshire, also the holders, choosing the right time and place to confirm their superiority in one-day competitions.
At one stage Hampshire looked like losing when they were 128 for 6 in the 28th over, chasing 220 for victory, and it was then that Zimbabwean Ervine proved his worth in a match-winning stand of 71 for the seventh wicket with his captain Dimitri Mascarenhas, who is in his last season with the club.
Ervine and Mascarenhas took the score to 199 in the 37th over before Mascarenhas holed-out to Tim Linley but Chris Wood joined Ervine in striking some telling blows as Hampshire made light of the remainder of their target. Ervine made his runs off 63 balls and struck nine fours as Hampshire eased home, but there had been plenty of scares along the way before they could be sure of their eighth win in 10 group fixtures.
Surrey, put into bat, made an inauspicious start, losing their first four batsmen for 39, two of them to Mascarenhas, while all-rounder Ervine reduced Surrey to 79 for five when he removed Gary Wilson in the 19th over.
Surrey managed to put together a competitive 219 for 9 only because of two major stands, of 66 for the sixth wicket between Rory Burns and Zafar Ansari and 53 for the seventh between Ansari and Linley. Ansari provided the backbone to Surrey's total by making 62 in an innings which included a six off Liam Dawson and five fours while Sohail Tanvir, Mascarenhas and Wood each took two wickets for Hampshire.
Hampshire have relied heavily on their opening pair of James Vince and Michael Carberry in one-day matches this season but within eight balls both were out, Carberry caught behind to Chris Tremlett's third ball of the innings and Vince caught and bowled by Jon Lewis to the eighth.
Neil McKenzie and Jimmy Adams began a rally with a stand of 55 for the third wicket but at the halfway point, Hampshire were struggled to keep up with the run rate at 68 for four, still needing 152 at more than seven an over.
Dawson began the Hampshire acceleration with a brisk 40 only for Adam Wheater to be run out the ball after Dawson had been bowled by Zander de Bruyn, reducing Hampshire to 128 for 6. It was then that durable veterans Ervine and Mascarenhas came together, taking control of the bowling and using the experience accumulated over many years of just such situations to see Hampshire home.