William Porterfield was the match-winner as hosts Birmingham Bears defeated Surrey by 16 runs to book their place in the showpiece at NatWest T20 Blast Finals Day.

Ireland captain Porterfield took centre stage in the first semi-final at Edgbaston with a wonderfully composed 81 not out from 47 balls, outshining team-mate Ian Bell's 38 and leaving Kevin Pietersen disappointed on his return to county cricket.

Pietersen managed a scratchy 13 as the Brown Caps failed to chase down the Bears' 194 for four, though had Jason Roy stayed much longer they might have had a chance.

Roy needed 50 to set a new record for runs scored in an English Twenty20 season and promptly reeled off 58 in just 28 deliveries but departed before the job was done.

Warwickshire got the day started at a brisk pace, form batsman Varun Chopra and returning England star Bell putting on 57 inside six overs.

Both men were quick to hit their stride, with Bell taking an immediate liking to Jade Dernbach, whose first two overs disappeared for 26.

Bell had struck four fours and two booming straight sixes when he jammed a Matt Dunn yorker into his stumps.

Chopra followed for 23 when veteran spinner Gareth Batty flung out a hand to claim a fine caught and bowled with his fifth ball.

That left Porterfield and Rikki Clarke at the crease and the pair were initially pegged back by Surrey's bowlers.

But from 80 for two at the halfway stage, the pair added 59 in the next six overs including four sixes - Clarke's blow over extra cover the most pleasing and Porterfield's onside cart off Dunn the biggest.

Clarke was third man out when he lobbed Robin Peterson down the ground for 35 but Porterfield continued in the same vein.

Porterfield faced 12 balls after Clarke's dismissal, scoring 29 runs - 14 of them in a poor final over from Dernbach, who shipped 56 from four overs.

Surrey's chase began at lightning pace, Roy hitting five fours and a six off Clarke's second over as the Brown Caps reached 50 in only 23 balls.

Roy's own landmark followed close behind after back-to-back boundaries off Boyd Rankin - his 19-ball half-century equalling the Finals Day record and apparently setting up his side for a big win.

But a top-edge off Jeetan Patel ended his fun and Surrey never got back on track, closing well short on 178 for seven.

Ateeq Javid held a sharp return chance to see off an awkward-looking Pietersen then accounted for Gary Wilson in his next over, while messy run-outs for Steven Davies and Kevin O'Brien essentially settled matters.

Chris Woakes cashed in at the end by cleaning up Azhar Mahmood and Robin Peterson, with Birmingham Bears reaching their first final since the inaugural competition in 2003.