Blues playmaker Stephen Brett believes speed off the defensive line will be the key to shutting down the Queensland Reds' attacking threats in the Super Rugby semi-final in Brisbane on Saturday night.

The pairing of five-eighth Brett and halfback Alby Mathewson will be crucial at Suncorp Stadium as they go head-to-head with Wallabies kingpins Quade Cooper and Will Genia.

Brett said allowing Cooper and Genia to guide their teammates to good metres over the advantage line would make the Reds hard to stop.

"If we can stop them, eliminate them, then hopefully it's going to be an even game," Brett said.

"The key is just line speed, getting up on them, putting a bit of pressure on them, and whenever their forward runners come around, just try to get them back behind the gain line."

The Blues also know they need to make a better start than in their defeat to the Queenslanders at the same venue last month, when they were down 24-0 after just half an hour.

They did manage a comeback to claim two bonus points, but the 37-31 result allowed the Reds to leap over them to the top of the table.

The Blues began slowly again in their semi-final qualifier against the NSW Waratahs in Auckland last Friday, before grinding out a 26-13 win.

Brett cited missed tackles on both occasions as being costly, and put his hand up for the ones he failed to nail against the Waratahs.

Brett, 25, had playoff experience with the Crusaders before moving to Auckland prior to the start of the last season.

The Blues are due to name their side on Wednesday, a day before the Reds, who have winger Digby Ioane, centre Anthony Faingaa and flanker Beau Robinson back from injury.

Brett said Ioane's strength and elusiveness made him a difficult opponent to stop.

"He probably benches about 180kg and squats about 240, so he's a pretty powerful and explosive man, and he's got good feet as well," he said.

"But, as I said, if we get good line speed against them, hopefully that will eliminate that."

Meanwhile, Brett revealed he and Cooper had been trading "a couple of cheeky comments" on Twitter.

"We've been giving a bit of grief to each other," he said.

"He's a good player and I enjoy playing against him. I've played against him a few times now and I guess it's just whatever five eighth steps up to their game."

The Blues leave for Brisbane on Thursday, a day earlier than they did ahead of their loss in May.

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