IF this was a dress rehearsal, only one side looked the part in their costumes.

St Johnstone eased to as comfortable a victory as they could have ever imagined against Dundee United, brushing aside their Scottish Cup final opponents with a performance full of power, pace and penetration. What Tommy Wright wouldn't give for a repeat on May 17 at Celtic Park.

"This will have no bearing on that," cautioned the Perth manager, but three victories in four meetings with Jackie McNamara's side this term cannot be considered as anything other than encouraging for St Johnstone, who have now won nine of their past 14 matches and move within three points of United in the Premiership table.

While the paucity of the visitors' display was a shock, it was no surprise that Stevie May was integral to St Johnstone's success. The 21-year-old had hitherto scored all of his team's Tayside derby goals this season and, although only one of yesterday's efforts was scrawled by his signature, his imprint was all over this match.

For much of the game, it had seemed that a 26th goal of the season - and a club record in the Premier League era - would elude him as a succession of chances came and went. First, May latched on to a long ball, breenged past John Souttar and shaved a lick of paint from the top of the crossbar, then he scudded another drive against an upright after a loose ball bounded into his path. A third miss, lifting David Wotherspoon's through ball over the crossbar, was the most glaring of the lot.

May would not be denied his fifth Tayside derby goal of the term, though. Wotherspoon and Dave Mackay combined on the right and, although Keith Watson initially reached the cross first, the ball broke clear for the striker to roll it over the line.

"The only thing I could criticise them for was not scoring more than two," said Wright.

Regardless, May's incision only served to bleed the last of United's hope. It had been dwindling ever since St Johnstone established an advantage just after the half hour as the visitors fell victim to a familiar frailty. Keith Watson conceded a silly free-kick in the right-back area and Wotherspoon's delivery towards the back post found Steven Anderson ambling into space to head past Radoslaw Cierzniak.

For McNamara, it was jarringly familiar but the fact United only trailed by one at the interval was perhaps fortunate.

Cierzniak had to paw at an Anderson volley in the first few minutes, and Watson had to howk a low Wotherspoon cross out from under his own crossbar. Paul Paton was required to do likewise after the interval and it had looked for all the world that Wotherspoon had gilded a splendid solo showing by scoring, only for his low effort to catch the inside of an upright and spin away to safety. Such profligacy would not matter, though, given how impotent United were. Despite having won nine of their previous 12 games, their defence often appeared on the brink of calamity, their central midfielders were overrun and their front four struggled to interact and impact on the St Johnstone back four.

Consequently, chances were scarce. Nadir Ciftci lashed wide after Gary Mackay-Steven burrowed into the box, Ryan Gauld prodded into the grasp of Alan Mannus, and Gary Mackay-Steven was also thwarted by the goalkeeper after attempting a cute lob. Ryan Dow was errant with two second-half shots.

Mannus would make an even better save in the final knockings, miraculously batting Brian Graham's close-range header clear but, by then, a goal would have been little more than a consolation. "We came looking to chase the teams above us," said United assistant manager Simon Donnelly. "But the quality of our play was disappointing."

Second place, and most likely third, too, appear out of United's reach now, with the gap to Aberdeen 10 points and Motherwell seven. Their focus will surely shift to the cup final and ensuring they are not afflicted by stage fright when these sides meet again next month.