Fly-half Danny Cipriani claimed a 21-point haul as Diamond's men kept alive their hopes of reaching the knockout stages of the Anglo-Welsh tournament with a 36-17 triumph.
Diamond, whose side travel to Wasps next week knowing victory could take them into the semi-finals, said: "We had to get four tries if we are to have any chance of progressing. We can't bank on just going to Wasps and winning - we're not good enough to do that. We've got to go down there, play well and try and get a result. That could be enough."
Diamond revealed skipper David Seymour had suffered no serious injury after he picked up a heavy knock and was replaced in the first half.
Cipriani crossed for a try, two conversions and four penalties in addition to further tries from Richie Vernon, Charlie Amesbury and Charlie Ingall.
Diamond added: "Danny is a good player. Give him go-forward ball, as the pack did, and he shows his class."
Scarlets head coach Simon Easterby took the positives from his side's first-half display before they gradually fell away after Jake Ball and Rhodri Jones were sinbinned either side of the break.
Easterby said: "We just dropped off second half, lacked composure and they got on a roll.
"We're missing 25 or 26 players but it is what it is. We know we have a large contingent in the Wales set-up, so this is an opportunity for younger boys to go out and show what they can do.
"I thought they went well, so there were some certainly individual positives to take from the first half in particular."
- Sports & Recreation
- Danny Cipriani