Paul John’s men kept their hopes alive of an historic double, which would see them become the first side to win the league and cup two seasons in a row.
Ponty avenged their 2012 final defeat at the hands of Keys with tries from James Howe and Gavin Dacey and 11 points from the boot of Simon Humberstone.
Nathan Trowbridge scored a try to lift his team’s hopes of victory, but the Keys couldn’t force their way past strong Pontypridd defence.
Fly-half Dorian Jones thumped Cross Keys into the lead after 10 minutes. But his counterpart Humberstone, who played in the Blues victory over Connacht less than 24 hours before, slotted a penalty two minutes later to level the scores.
An electric break from Ponty wing Lewis Williams almost gave his side the lead before the Principality Premiership leaders rumbled over for their first try.
Locke collected Aled Morris’s line-out throw and the Pontypridd pack shunted Howe over the line to score and boost his team’s hopes of a second double in as many seasons.
Jones had the chance to pull Ponty’s lead back to two points after the men from Sardis Road were caught offside. But the Keys kicker saw his long-range shot drop just short.
Keys scrum-half Rhys Dyer was then penalised for obstruction as Elliot Jones sliced through the defensive line.
And Humberstone stretched the Valley Commandos’ lead to eight points three minutes from half-time with a 45-metre penalty.
The Ponty stand-off kept the scoreboard ticking over with a well-timed drop goal to give his side a 14-3 advantage just after half-time.
The decisive score came through centre Dacey after 62 minutes.Man-of-the-match Geraint Walsh found talismanic captain Dafydd Lockyer running a dangerous angle, he sliced through and picked out Dacey who crashed over from five metres out.
Cross Keys hit-back just three minutes later to prove they were far from finished. Replacement scrum-half Trowbridge sniped through a gap in the defence to score – but Steffan Jones missed the conversion.
