Callum Booth's first goal for St Johnstone sent the Perth side on their way to a 3-0 William Hill Scottish Cup win over Morton in a match held up by floodlight failure at McDiarmid Park.
Booth curled home from long range in the fourth minute before the second half was delayed by about 25 minutes.
Morton started well but goals from Murray Davidson and Stevie May eased Saints into the fifth round.
Saints took the lead after Drey Wright made progress down the right and cut the ball back. May's blocked shot fell invitingly for Booth 25 yards out and the left-back curled into the top corner with his right foot.
The visitors had a swift chance to level when Reghan Tumilty found Luca Colville 12 yards out but the midfielder shot well over.
Danny Rogers kept Morton in it when he pushed over Davidson's deflected cross but the visitors had the better of the chances before the second goal.
Zander Clark spilled Nicky Cadden's shot but his defence cleared and Wright's misplaced pass almost sent Robbie Muirhead in, but the striker could not make contact with the ball.
Problems with the floodlights were apparent in the first half and they went off at half-time, soon after coming on. With the sunshine making way for dusk, the teams stayed in until the lights came back on and the game eventually got back under way.
Morton emerged the livelier team and Clark made saves from Tumilty, Kyle Jacobs and Brian McLean in quick succession.
But the hosts doubled their lead in the 57th minute when Davidson rose well to loop a header into the top corner from Wright's corner.
May forced a good save from Rogers before latching on to Anthony Ralston's long ball and knocking it past the goalkeeper in the 74th minute.