Cardiff got off to a bright start thanks to flying winger Jimmy Norris who raced 40m to see his try converted by Gareth Davies. But the Blue & Blacks game then fell apart as basic errors and poor discipline gave Keys a way back in.
Gareth David banged over six shots at goal, including three in seven minutes, as Cardiff struggled to look like championship contenders. Two penalties by Davies ensured Cardiff were only two points behind at the break but any thoughts of starting brightly in the second half were dismissed when flanker Jamie Ringer was yellow carded.
The home side then hit a purple patch while Ringer was having a rest on the sidlelines. Davies knocked over a penalty and added a conversion to Craig Morgan's try after the former Welsh winger intercepted on halfway and raced clear.
Groves hit back with his brilliant individual effort converted by David but Cardiff edged 32-25 ahead with two further Davies penalties. With only seconds remaining, Cross Keys then stunned Cardiff with a sweeping 70m move which saw Matthew Pewtner score. David added the conversion to secure the first draw in the Premiership of the season.