Seventeen-year-old Kallum Watkins enjoyed a memorable tryscoring debut for Leeds as the world club champions booked their place in the fifth round of the Carnegie Challenge Cup.

Watkins, who turned 17 only last month, and academy team-mate Ben Jones-Bishop, who was named man of the match on his debut, both seized their opportunities to help keep the under-strength Rhinos on course for Wembley.

But they were forced to work hard for most of their fourth-round tie as Celtic Crusaders pressed their claims for a place in Super League.

The Welsh club, who are one of 19 applicants for a Super League licence for 2009, did not look out of place at Headingley and trailed only 14-10 at half-time before eventually being overpowered by the competition's joint favourites.

Leeds, lacking six internationals through injury, gave debuts to three teenagers who all acquitted themselves admirably as the home side raced into a 14-0 lead inside 20 minutes.

Full-back Jones-Bishop, 19, supported a break by Danny McGuire to set up the position for the impressive Watkins to get right winger Lee Smith over for the game's opening try on seven minutes.

Left winger Scott Donald took his try tally to 14 in 13 appearances before a delightful pass from Jones-Bishop released centre Keith Senior and scrum-half Rob Burrow was on his shoulder to claim the Rhinos' third try.

Kevin Sinfield kicked the first of four goals to make it 14-0 but the Crusaders battled admirably and experienced scrum-half Jace Van Dijk caused some anxious moments in the Rhinos defence with his clever footwork and varied kicking game.

And they briefly closed the gap to just four points thanks to a two-try burst from Welsh international winger Anthony Blackwood in the second quarter.

Former Hull KR prop David Tangata-Toa combined with centre Mark Dalle Court to get the former Halifax player over on 28 minutes and he grabbed his second seven minutes later courtesy of a cut-out pass from Van Dijk.

Mark Lennon added one conversion to make it 14-10 at the break but it took the Super League champions just three minutes of the second half to reassert their authority, McGuire's jinking run creating a try for hooker Matt Diskin.

McGuire then finished off a searing break by Burrow and Watkins burst through a two-man tackle for a memorable score.

Senior then proved unstoppable form 10 metres out and Burrow added a touchline conversion but the brave Crusaders had the final say when Dalle Cort forced his way over for a third try six minutes from the end and Lennon kicked his second goal.

The Welsh side battled to the end and Blackwood almost completed his hat-trick in the final minute, reaching the line only to be turned on his back.