Somerset 317 and 194 for 9 (Overton 40*, Shakib 4-83) lead Surrey 321 (Curran 86, Patel 70, Vaughan 6-102) by 190 runs

Making his first appearance in the competition for two years, the all-rounder smashed eight sixes and six fours in a game-changing innings of 86 from 75 balls, which rescued the Division One leaders from a perilous 228 for 8 in their first innings and allowed them to post 321 all out.

Craig Overton was unbeaten on 40, having added 41 for the last wicket with a stricken Tom Banton (28 not out), batting heroically with a runner after suffering an ankle injury playing football in the warm-up for the day's play.

Only the most optimistic of Surrey fans could have expected a first innings lead when their team lost five wickets for 32 runs from a promising 196 for 3. Ryan Patel had added nine to his overnight score of 61 when top-edging a sweep off Leach to short third-man.

Shakib made 12 before being caught and bowled by Leach off a leading edge. Then Vaughan added to his three second day victims by having Ben Foakes caught at short leg for 37 off 122 balls.

It was 228 for 7 when Jordan Clark chipped a catch to the diving Tom Abell at mid-wicket off Vaughan, who struck again two balls later as Cameron Steel played down the wrong line and was bowled off stump.

Surrey trailed by 89 runs. But Kemar Roach played a key role in contributing just five runs to a stand of 54 with Curran, who had begun his blitz with a six over long-on off Vaughan.

Two more maximums off the same bowler followed by a four through the covers took Surrey to their first batting point and the all-rounder was far from finished. When Somerset skipper Lewis Gregory took the decision to remove Vaughan from the attack and introduce part-time spinner Lewis Goldsworthy, the left-armer's only over went for 18 runs.

The first ball was a full toss, dispatched over the mid-wicket boundary by Curran, who followed up with two straight sixes of the fourth and fifth deliveries. The story of the day was being transformed and by the time Roach was pinned lbw by Leach, Somerset's lead was only 35.

Still Curran ran riot, a six off Leach taking Surrey to a second batting point, celebrated by another six in the same over. A four off Vaughan gave the visitors the lead before the memorable exhibition ended with a skyed catch to long-on.

Surrey team-mates gathered on their dressing room balcony to cheer Curran off the field, while Vaughan followed holding up the ball to acknowledge applause for his outstanding contribution to Somerset's bowling. Lunch had been delayed and was taken between innings.

Momentum was with Surrey and their bowlers soon increased it, reducing the hosts to 85 for five by the time rain forced an early tea. Vaughan was bowled playing around a delivery from Shakib and it was 12 for 2 when Goldsworthy suffered the same fate attempting to pull a short ball from Roach.

Shakib claimed the key wicket of Tom Abell, lbw for 18 and, with Banton absent, Jordan Clark bowled Kasey Aldridge with his second ball of the innings before pinning Tom Lammonby LBW for 24.

The final session, starting at 4.05pm, saw Gregory fall leg-before for 13, pushing forward to Shakib after a stand of 35 with Rew, whose composed innings of 29 ended when he edged the Bangladesh left-arm spinner to Dom Sibley at slip.

Brett Randell fell cheaply and when Curran's great day continued by having Leach caught behind for 13, Banton hobbled painfully and slowly to the crease with the total 153 for 9.

Incredibly, with little or no foot movement, he struck four fours in helping Overton give Somerset genuine hope for the final day.