Arthur Numan struck again at a blustery McDiarmid Park last night as Rangers cruised into the fourth round.
The Dutch defender scored his first goal for the Ibrox club against Aberdeen eight days ago and arrowed in another from the edge of the area four minutes before the interval.
Fellow countryman Giovanni Van Bronckhorst doubled Rangers' advantage midway through the second period as the visitors exploited the driving wind and rain to maximum advantage.
Saints never remotely threatened a shock win after Nathan Lowndes' 14th-minute effort, and once the visitors took the lead, the game's destiny was determined.
With Billy Dodds suspended, Rangers coach Dick Advocaat turned to veteran striker Gordon Durie to partner Rod Wallace up front.
Tugay Kerimoglu was again on the bench but the Turkish international was probably thankful as the driving wind and rain were hardly the most appetising of conditions in which to make a debut.
Celtic expect tomorrow's friendly fixture with Bayern Munich to go ahead despite the storm damage which forced Saturday's tie with Inverness Caledonian Thistle to be postponed after one of the stands was ruled unsafe.
St Johnstone: Main, Weir, O'Neil, Kane, Lowndes (Simao 57), Bollan, Griffin, O'Halloran, McBride (McAnespie 69), Dods, Jones. Subs Not Used: McCluskey.
Rangers: Klos, Moore, Amoruso, Numan, Ferguson, Kanchelskis (Reyna 83), Van Bronckhorst, Wallace (McCann 67), Albertz (Kerimoglu 81), Vidmar, Durie. Goals: Numan 42, Van Bronckhorst 65.
Referee: J Rowbothan (Scotland).
