Rhinos face St Helens in the first Carnegie Challenge Cup semi-final, at Galpharm Stadium, Huddersfield, tomorrow.

Saints have been in unstoppable form over recent weeks, scoring 214 points in their last four games.

Senior reckons Leeds need to be at their absolute best – and he said they must play with their heads as well as their hearts.

"It'll have to be a near-perfect performance," said Senior.

"We can't afford to make errors, because Saints are a very dangerous side.

"We can't afford to play the game in our half, so we've got to play with our brains as well as using brawn. It is going to be a really tough game and an exciting one and it's one to look forward to.

"Whoever wins on the day is going to have to play to the best of their capabilities."

Senior admits Saints have been in better form over the season half of the campaign, but he feels a Leeds win tomorrow would transform the Headingley outfit's season.

"They are definitely on form," he said. "They've won 15 games on the bounce, so you'd definitely say they are the form team.

"That was us at the beginning of the season, but they've overtaken us in the form stakes and we've been a bit up and down, which is something we've got to address.

"But you can't go all season being perfect. It's better to have a little blip in mid-season rather than when it comes to the business end of the year.

"We can turn the season around just by winning this one game."

A spell of three defeats in four games saw Rhinos squander a six-point advantage at the top of engage Super League, but they've won their last two in impressive fashion and, according to Senior, that has provided a timely confidence boost.

"It was a really tough game against Catalans last Saturday," he said. "They deserve their position in third spot and it was a great game for us, it was a tough, competitive game that we had to grind out, which you could say was better for us than the game that St Helens had – a 40-point win against Wigan.

"We have shown we can play in these tough games and we can grind out these wins, which is important coming into this sort of game."

Senior is the only player in the Leeds squad to have appeared at Wembley, after being a member of the Sheffield Eagles team which stunned Wigan in one of the all-time great upsets a decade ago.

"There's only two major domestic trophies to be won and this is one of them," he said.

"It's steeped with history and the final is a massive occasion and a very enjoyable one, especially with it being at the new Wembley.

"I was lucky enough to play at the old one, but the Challenge Cup is something that's eluded me with Leeds, I've had three Challenge Cup final losses, so it's massively important for me to get there and achieve the Challenge Cup with Leeds.

"At the beginning of the season we target everything and to keep on track for our goals, it's a must-win game on Saturday.

"The boys are fired up for this game and really looking forward to a tough, competitive battle."

Full-back Brent Webb is back in contention for Rhinos after missing last weekend's win over Les Catalans Dragons due to a back injury.

Prop Ryan Bailey (ankle) remains on the sidelines and back-rower Jamie Jones-Buchanan is ruled out after injuring a hamstring in France.

His place in the squad is taken by Simon Worrall and Luke Burgess – 18th man last week –could feature tomorrow.

Saints boss Daniel Anderson will select from the 17 on duty in last weekend's win over Wigan, plus forward Paul Clough and half-back Kyle Eastmond.

Leeds Rhinos from: Smith, Hall, Toopi, Senior, Donald, McGuire, Burrow, Leuluai, Diskin, Peacock, Ellis, Lauitiiti, Sinfield, Scruton, Ablett, Kirke, Burgess, Webb, Worrall.
St Helens from: St Helens: from Wellens, Gardner, Gidley, Talau, Meli, Pryce, Long, Graham, Cunningham, Hargreaves, Gilmour, Wilkin, Sculthorpe, Roby, Cayless, Flannery, Fa'asavalu, Clough, Eastmond.

Referee: Ashley Klein (Keighley).

Kick-off: Tomorrow, 12.15pm.