Perry Mason really did lose one case. But it was not the scenario where a conviction was overturned because the real murderer was identified (although that did happen once or twice!)
I remember taping a Perry Mason when in advance (a re-run) they advertiesed he lost the case, but it was the overturned or reversed scenario.
I finally did tape a Perry Mason where his loss is really documented....but it was as follows.....
The beginning of the episode has Perry somewhat informally chatting with the Judge played by Robert Middleton. The judge says something to the effect that he (Perry) could {maybe} have won if he had argued thus and so .....etc., ...then the episode develops into a new unrelated story, which of course Perry wins.
So Perry's only documented TV loss is a reference point, not an episode. I think more than one involved an apparent loss before the final winning resolution.
It was not Columbo's job to prosecute. In his own words in at least one episode he says it's someone else's job to prosecute, judge and sentence.
Technically Columbo and Mason weren't playing each other and the subject question is a moot point.....but what do I know....I'm just a hair splitter with too much time on my hands...bothered by all those little things