Birmingham 194 for 4 (Porterfield 81*) beat Surrey 178 for 7 (Roy 58, Javid, 2-13) by 16 runs

T20 cricket is generally regarded as a batsman's game, but it was an unheralded spinner who supplied one of the crucial contributions to help Birmingham into the final of the NatWest Blast in front of a full house at Edgbaston. It is the first time they have made it into the final since the first year of the competition in 2003.

Perhaps it is wrong to describe Ateeq Javid as an offspinner. Certainly he bears little in comparison to Jim Laker or Graeme Swann. He is, in effect, more of a mid-innings spoiler, though such a title sounds unflattering and does little to reflect his worth, in this format at least.

Javid, a 22-year-old born a few miles from Edgbaston in Aston, developed through the youth system and signed as a batsman. But his spin bowling, mean and quick and flat, has proved ever-more useful in this format and his three overs here conceded only 13 runs and brought two wickets.

In a game when nearly every other bowler suffered painful figures, it was a spell that went a long way towards suffocating a Surrey innings that had seemed on course for success at the halfway stage of their innings. He now has the best economy rate - just 5.65 runs per over - of any bowler in the competition who has delivered more than 22 overs.

Surrey started brilliantly. Jason Roy, the highest run-scorer in the competition this season (he finishes with 677 runs at an average of 48.35 and at a strike-rate of 157.07), provided another nudge to the England selectors with a ferocious 19-ball half-century that saw Surrey plunder 88 runs from the first seven overs of their reply. "Had he been in another five overs, they would have had it won," Varun Chopra, the Birmingham captain, said afterwards.

He thumped 26 off Rikki Clarke's second over - five fours and a six - showing once again his power, his range of stroke and his fine eye for the ball. It seems unthinkable the England T20 side can do without him ahead for the one-off match against India at this ground in a couple of weeks.

"He has been the best player in the competition this season," Gary Wilson, the Surrey captain said. "I would be very surprised if he is not called up by England soon."

But once he fell, top-edging a slog-sweep off the ever-impressive Jeetan Patel, the Surrey innings stalled in the face of some decent bowling from Boyd Rankin and the excellent Javid.

Perhaps the killer blows were struck when he had Kevin Pietersen caught and bowled with a sharp return chance and then had Gary Wilson caught at cover off a leading edge. By the time Azhar Mahmood was bowled round his legs by the sharp-looking Chris Woakes and Kevin O'Brien was run-out attempting a second, Surrey were doomed.

But it was a brutal innings of 81 from William Porterfield that set-up the Bears's challenging total. While Porterfield struggled for the first half of his innings - he took 26 balls over his first 20 runs - he thrashed 61 off his final 21. Crucially, Warwickshire took 37 from the final two overs of their innings bowled by Mahmood (who conceded 18) and Dernbach (who conceded 19).

"It was right up there with the most pleasing innings I've played for Warwickshire," Porterfield said afterwards. "Coming in with only two balls of the power-play left, we had to set it up, lay a platform and then step it up later."

But Surrey will reflect that they made life a little too comfortable for their opposition. Not only was Porterfield dropped on 41 by Robin Peterson at cover - a relatively straightforward chance - but their bowlers served up an alarming number of full tosses.

"Azhar and Jade have been excellent all season," Wilson said. "But you can't turn it on every day and today it just didn't come off. If we're really honest, we didn't hit our lengths at all. They got about 15 too many. We weren't good enough all round."

Birmingham were given a bright start by Ian Bell. He had not played for Warwickshire in this format since 2010, but looked in fine touch as he made 38 in just 17 balls. Their progress was slowed considerably by the introduction of the Surrey spinners. Gareth Batty and Robin Peterson conceded a relatively frugal 56 runs in their eight overs; just 13 more than Matt Dunn in his four overs.

Batty was particularly impressive, conceding only 24 and claiming an outstanding one-handed catch off his own bowling to dismiss Varun Chopra. But the seamers were unable to retain the same control and, for the second successive year, Surrey were forced to reflect on failing to chase 194 on Final Day, having last year failed to overcome Northamptonshire's total in the final.

Birmingham needed to win their last three group games to sneak into the quarter-finals. But now, with five wins in succession, they might just consider themselves the form side going into the final in front of their home crowd. Bell was among a group of players who was mulling the idea of a round of golf at nearby Edgbaston Golf Club in between games.

Jonathan Trott, who was not selected despite having scored two centuries in his last four List A games, spent the morning having a long net with Graham Gooch instead.

George Dobell is a senior correspondent at ESPNcricinfo