Rob Miller's late try secured a vital four points that have kept their European hopes alive.
"We're delighted with the win," said Diamond.
"We've done a lot on our defence and it showed in the last 15 minutes that they've been listening to what we've been doing in training.
"At this end of the season, if we can scrape into Europe, then they're the four points that might help us get there."
The Sharks have moved up one place in the Aviva Premiership table to sixth following the win.