Danny Brough gets to grips with Bradford's Glenn Morrison

Cas, relegated last season from Super League, were 18-6 down at half-time but tries from Michael Shenton and Peter Lupton gave them a chance.

But David Solomona steadied the Bulls nerves with a try and they held on.

Elsewhere, there were comfortable victories for holders St Helens, Leeds and Salford.

Saints were barely troubled against Batley, running in 14 tries in a 78-14 win with two apiece from Paul Wellens, Francis Meli, Lee Gilmour and Maurie Fa'asavalu while teenager Steve Tyrer kicked 11 goals.

Captain Paul Sculthorpe missed the game but coach Daniel Anderson said he would feature in the Good Friday clash with Wigan at the JJB Stadium.

There was speculation that the Leeds players wouldn't respond well to my new position but they showed their intentions Leeds and new GB coach Tony Smith

Leeds were equally dominant against Workington, winning 72-10 with Scott Donald managing four tries and Rob Burrow scoring a hat-trick.

It was the Rhinos' first action since the enws that their coach Tony Smith had been appointed to the Great Britain job.

"There's speculation about my new position that the Leeds players wouldn't respond well to it," said Smith.

"I think they were quite hurt by that and they showed their intentions that we're here as a group and looking to do something special for the rest of the season.

"I think that was a fair statement out there and it probably answers all those people who may have doubted our intention for the remainder of the year."

Luke Robinson scored four tries as Salford swept aside Gateshead 64-4 to go into the hat for the next round.

Bradford had looked on course for a comfortable win against Castleford when they went over for a try within two minutes through Glenn Morrison but winger Michael Wainwright levelled it up after nine minutes.

Tries by Marcus St Hilaire and Lesley Vainikolo, both converted by Paul Deacon, kept the Bulls ahead and they appeared set for a comfortable passage into the next round.

But Castleford were not going to give up without a fight with Awen Guttenbeil and Danny Brough leading the charge and Shenton was rewarded with a try to cut the gap.

Brough then set up Lupton to give Cas the chance of an upset but when Solomona went over with just over 10 minutes to go, the Bulls dug deep to hold on for the victory.

In the first half I thought we were pretty ruthless Salford coach Karl Harrison

Bradford coach Steve McNamara afterwards admitted he was very relieved after his side's victory.

"I'm happy to be in the next round," he said. "It got a bit hairy but I always thought we had it in us to win the game.

"We weren't great but the game was played at a terrible pace. It was a million miles off how we can play but I'm happy we've got past a potential banana skin."

But the Bulls were given an injury scare when hooker Terry Newton and winger Lesley Vainikolo were forced off before half-time with arm and groin injuries respectively.

"There was no point risking them going back on," said McNamara.

Castleford coach Terry Matterson was delighted with his team's efforts but critical of the display of referee Ashley Klein.

"I've got 17 disappointed guys in there," he said. "We came here confident we could cause an upset.

"We like to play footie but we weren't allowed to do that. One side were allowed to lie on and it was really frustrating.