Coach Mark Robinson insists Sussex will continue to tinker with their tactics as they search for a winning formula in Twenty20 cricket.

The Sharks sprung three big selection surprises during Tuesday's win over Essex but they all paid off.

Chris Nash was promoted to open and smashed 24 off 17 balls, all in boundaries, while Robin Martin-Jenkins justified the decision to give him the new ball by taking 2-21, his best figures in the competition so far.

And Saqlain Mushtaq bowled four tidy overs of off-spin on his debut as Sussex won by 16 runs to move into second place in the south group.

Victory against Surrey at the Oval tonight (5.40pm) would almost certainly guarantee their place in the quarter-finals for the first time and, even if they lost, there would be a second chance of progressing at home to Hampshire on Friday.

Two third-placed sides in the three groups also go through. Robinson said: "Our Twenty20 side is still evolving. It is easy to forget that we are missing Matt Prior, who is one of the best one-day players in the country, and Mike Yardy, who was our best player in Twenty20 last season.

"So we have had to adapt a bit but I thought Tuesday was our best all-round performance so far and it will give us a big springboard for the last two games.

"Nashy made his first proper contribution in Twenty20 and that was great for him.

"I just felt we needed a bit more depth in the batting and it was a big moment in the game when he got off the mark with a six off Andy Bichel.

"We knew we would be in a good position if we bowled well. Essex batted really well up front with Bopara and Flower and they kept coming at us. But when the pressure was on, Martin-Jenkins and James Kirtley bowled brilliant overs.

"We wanted Robin to be more aggressive and he did it. There was a bit of dew on the ground and he got the ball to really go through. We need him to do the same again tonight but he has been bowling well all season to be fair."

Four sides are chasing two guaranteed quarter-final places in the south group and Robinson recalled that Sussex were in an even better position to go through a year ago, only to lose their last three matches when only one win was required.

"It's a dog eat dog group," he added. "One minute you think you are a great team and then all of a sudden you are brought back down to earth. Anybody can beat anybody and we are very mindful of what happened last season. With the age spread of this team there are going to be some massive highs and lows and occasional inconsistency.

"But we have definitely improved as the competition has progressed and I hope Tuesday's win will give us real momentum."

It will be an emotional return for Saqlain, who helped Surrey win three Championships and a one-day trophy during his career at the Oval. The Pakistan off-spinner is hoping to put local knowledge to good use.

He said: "I'm looking forward to going back to the Oval. I was in the gym yesterday but all the time I was thinking about the Surrey boys and hopefully I can pass on some knowledge.

"I played there for nine years so we know each other pretty well."

Surrey: Benning, Brown, Ramprakash, Butcher, Clarke, Batty, Schofield, Nicholson, Doshi, Dernbach, Saker.

Sussex: Nash, Goodwin, Wright, Adams, Hopkinson, Hodd, Rana Naved, Martin-Jenkins, Saqlain Mushtaq, Mushtaq Ahmed, Kirtley.

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