Trailing just 12-10 on the hour mark, they fell away badly in the final quarter having already squandered a raft of chances.
Carnegie had beaten Welsh 31-28 away in the Championship only last week but this defeat - on home soil at Headingley, too - ended a five-match winning sequence.
Their usually potent line-out drive was dealt with comfortably by the visitors and Redpath admitted: “We created opportunities, maybe about six, but didn’t take them.
“Fair play to London Welsh - they created and took every one they had a chance at.
“They played very similar last week so they didn’t surprise us.
“But we just took our opportunities then and didn’t here having come out in the second half and got back to 12-10.
“Welsh then grew in strength and that shows, when you’ve got half a dozen injuries as well, you do suffer.
“On a whole, one of our goals was to get to this final. Sadly, today it hasn’t gone our way but we’ve still got a game next week to focus on.”
Carnegie, whose sole try came from Chris Walker in the 43rd minute, play their penultimate Championship regular fixture at home to Nottingham next Sunday as they look to keep pressure on second-placed Doncaster Knights before the play-offs.
As disappointing as this final defeat was, Redpath insisted it would not derail their main bid of challenging for promotion.
“It’s not a massive loss,” he said. “We’d won five on the bounce and then suddenly lost one so it’s not a massive momentum swing.
“It’s just not our day today and that happens.
“Jack Walker is hopefully back in the mix next week, though, and it’d be great to get a few others back -Jonah Holmes, Andy Forsyth, Pete Lucock and David Doherty.”