A try from outside-half Jarrod Evans helped Cardiff Blues register their first win in Swansea for 14 years as the Ospreys woeful form continued with a 19-16 Guinness PRO14 Welsh derby defeat at the Liberty Stadium.
Evans provided 11 points – a try and two penalties – with replacement Jason Tovey kicking two penalties and a conversion.
Scott Otten made his 100th Ospreys appearance as one of six changes from the 40-27 loss against Racing 92 in the European Champions Cup.
Cardiff Blues handed wing Adams his PRO14 debut, although they were still without injured flanker Josh Navidi.
Ospreys ended the first half 10-6 up, with Blues having received two yellow cards and playing with 13 men for the final nine minutes of the half.
It was a cagey derby dominated by kicking in the opening exchanges, with McKenzie opening the scoring with a penalty goal on five minutes following a collapsed scrum.
But Blues went into the lead with two Evans penalties after 20 and 26 minutes as Ospreys struggled for the form which has eluded them for almost the entire season.
Their cause was not helped when McKenzie rattled the upright with a penalty attempt before Ospreys finished the half the stronger.
First Paulo was sin-binned for tackling Hanno Dirksen off the ball and then, more crucially, Williams went to the bin as referee Dan Jones awarded Ospreys a penalty try after the scrum-half had high tackled Dan Lydiate as he went for the line.
Matters were not going Blues’ way and that continued when Evans missed a kickable penalty in the final minute of the first half.
Blues suffered their third yellow nine minutes into the second half, with Adams sent to the bin for a professional foul allowing McKenzie to kick his second penalty.
But gradually Blues, who made some key substitutions including the injection of Olly Robinson, Tovey and Hallam Amos, eased into the lead through a Tovey penalty and a try for Evans who latched on to an inventive chip from scrum-half Williams.
McKenzie managed to level the scores at 16-16 with a 64th-minute penalty, but Tovey’s penalty goal after 74 minutes proved the decisive score.
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