Leeds fielded a patched-up side, including17-year-old debutants Max Simpson and Jack Sinfield, but hit back from 8-0 down to go into the final quarter all square.
The sin-binning of Leeds second-rower James Bentley proved costly, but they were in the contest until the final seconds.
A major concern for Rhinos was a head injury suffered by stand-off Blake Austin, which leaves them without any experienced half-backs for Friday's crucial visit of Toulouse Olympique.
Here's how the Rhinos players rated, plus marks for the Castleford side and referee.
A major concern for Rhinos was a head injury suffered by stand-off Blake Austin, which leaves them without any experienced half-backs for Friday's crucial visit of Toulouse Olympique.
7. Jack Sinfield (No 32)
For a 17-year-old in his senior debut, very assured and grew in confidence as the game went on 7. Photo: Allan McKenzie/SWpix.com
8. Mikolaj Oledzki (No 8)
Ran his blood to water, but found it tough as a lone specialist prop at times 7 Photo: SWpix.com
9. Kruise Leeming (No 9)
The captain had to switch into the halves early, but put in a big shift 7 Photo: Allan McKenzie/SWpix.com
10. Bodene Thompson (No 19)
Returned to the team in the starting lineup, but had a long spell off the field 5. Photo: Tony Johnson
11. James Bentley (No 11)
Played well, but costly penalty and sin-binning undid that good work 6 Photo: Allan McKenzie/SWpix.com
12. Reece Martin (No 12)
Couldn't have done much more, scored all Leeds' points with two tries and three goals 8 Photo: Allan McKenzie/SWpix.com