Rangers closed the gap on Scottish Premier League leaders Celtic to just one point following Saturday's 2-1 victory over St Mirren.
Walter Smith's side moved above Hibernian into second place in the table after taking advantage of Celtic not being in action until Sunday to keep the pressure on their Old Firm rivals.
The outcome at Ibrox was never in doubt after Kris Boyd fired them into a first-minute lead with a close-range strike.
Boyd's seventh league goal of the season in the 57th minute doubled the advantage and killed off any hopes mid-table Saints had of taking a point from their trip to Glasgow.
Stephen O'Donnell's 88th minute response for Saints was purely academic.
Earlier in the day, Hibs had opened the door to Rangers in the battle for second place after playing out a goalless draw with Hearts in disappointing Edinburgh derby at Tynecastle.
Hibs came closest to breaking the deadlock when Janos Balogh tipped David Wotherspoon's shot onto his post midway through the second half.
Elsewhere, Sone Aluke responded to criticism from manager Mark McGhee by firing Aberdeen to a 2-1 victory over St Johnstone.
The Nigerian winger's appetite was recently questioned by McGhee, but Aluke's 15th minute strike put the Dons into the lead at Pittodrie.
Liam Craig levelled the scores 14 minutes from time, before Lee Miller's penalty soon after secured only a second home victory of the season for the Dons.
Motherwell extended their unbeaten run to five games with a 2-2 draw against Hamilton.
Guillaume Beuzelin was sent off in the first half following two quickfire cautions and Simon Mensing's 61st minute goal put the Accies ahead.
Jamie Murphy made it 1-1 on 78 minutes before Marco Paixao thought he had won it for the home side four minutes later.
However, Lukas Jutkiewicz salvaged a point for the Steelmen with a late equaliser.
Dundee United moved up to fourth place in the table after a 2-0 victory over Kilmarnock at Rugby Park.
Damian Casalinuovo's 22nd minute penalty opened the scoring for the Terrors, before the Argentinian striker wrapped up the points with a 57th minute second goal.