Super League champions Leeds were made to work hard before beating Celtic Crusaders 38-16 to reach the fifth round of the Challenge Cup.

Leeds led 14-0 early on but two Anthony Blackwood tries helped cut the lead to 14-10 by half-time.

But Matt Diskin, Danny McGuire, Kallum Watkins and Keith Senior all went over after the break to seal victory.

Whitehaven also advanced to the next round after an easy 46-6 success over French League leaders Lezignan.

Leeds, who were without six internationals through injury, gave starts to teenagers Ben Jones-Bishop, who impressed at full-back and Watkins, who marked his debut with a try.

The Welsh side, who are one of 19 applicants for a Super League licence for 2009 can be pleased with their performance with Blackwood being denied a hat-trick in the final minute, reaching the line only to be turned on his back.

We were competing really well in the 80th minute and, as a coach, that's really pleasing Celtic Crusaders coach John Dixon

Leeds coach Brian McClennan paid tribute to the visitors afterwards.

"They played really well," he said. "They are well coached and have got good structure. Ten minutes before half-time they had us struggling.

"We knew they were a side who had got some good football in them and they got themselves up for the game."

Crusaders coach John Dixon was also delighted with his side's performance.

"Our fitness stood up and we held our shape," he said. "A lot of sides would have got beaten by 50 or 60 points tonight.

"We were competing really well in the 80th minute and, as a coach, that's really pleasing."