Rangers boss Giovanni van Bronckhorst said his side would go into the break in the place they wanted.
Scott Wright squeezed in an opening headbutt before Morelos slammed in a first-half goal.
The hosts did not add to their advantage after the interval.
"I'm happy with the performance, it was very controlled," he said.
The manager said that the score needs to be more when the chances are created. The movement and passing was good. We could've scored more, but we wanted to keep going and create chances.
Rangers have not lost in 27 home league matches since March of 2020 when they were beaten by Hamilton Academical.
If Celtic want to retain their title, they will need to drop the same figure in their final 18 games.
With their winless run stretching to 11 games, the ninth-ranked Paisley side are just three points off the play-off spot.
Reaction as it happened.
The fact that Rangers had won each of the last 10 top-flight meetings against St Mirren and their last eight on Boxing Day before the game was a bad sign.
Pressure was on Giovanni van Bronckhorst's men to restore their six-point advantage after Celtic's victory.
The bold attacking line-up the Dutch coach named was rewarded when Wright opened the scoring after a wave of early pressure.
The ex-Aberdeen forward was able to cross the line despite Jak Alnwick's best efforts.
Alan Power slipped in Curtis Main, who was chopped down byConnor Goldson on the edge of the box.
The Rangers defender was shown a yellow card by the referee.
The hosts continued to pepper the backline and doubled their advantage when Morelos found Borna Barisic.
The rebound fell into the path of the forward, who blasted in a second after forcing the keeper to make a good save.
After the break, it was more of the same, with Alnwick denying Morelos before smothering a Joe Aribo effort.
Barisic and Ianis Hagi both saw efforts fly off target, while Wright was inches away from adding a third when the game's opening goal was scored.
11 men were on the park when James Tavernier's upper thigh was hit by a studs from Ethan Erhahon.
The Rangers captain missed a half volley that was parryed away by the keeper, before Morelos and Scott Arfield missed chances to add a third.
The league leaders would have liked to have scored more in the second half, but three points is all that matters as the hosts go into 2021.
The man of the match was Alfredo Morelos.
The Colombia forward has six goals in his last eight games and was at his best in the first half.
What did we learn?
All you have to do is look at Wednesday to see the difference between Rangers and Celtic.
Celtic's lack of options resulted in them dropping two points in Paisley, while Van Bronckhorst's long list of attacking talent allowed him to blow away Goodwin's side early.
A number of players are getting back to their best under the 46-year-old, who has won his first seven top-flight games.
February's Old Firm derby looks like it could be a title decider even at a relatively early stage. A six-point gap looks steep.
The break will allow the side to get bodies back for a big second half of the season as they look to pull away from the foot of the table.
What's next?
On January 18th, both Rangers and St Mirren will play their first games of the new year, as they travel to Aberdeen and Dundee United, respectively.
The Rangers are a team.
St. Mirren
Line-ups.
Match statistics.
Live text.
Formation 4-3-3.
2Tavernier6Goldson3Bassey31Barisic
McGregor is a person.
2Tavernier
The book was written at 23 minutes.
3Bassey.
31Barisic
Substituted forSakalaat.
18Kamara.
17Aribo
23Wright.
20 Morelos.
Substituted forArfield at the end.
Substitutes.
10Davis
15Simpson.
16Patterson
22Bacuna.
30Sakala
McLaughlin is 33
37Arfield
Formation 4-5-1
Fraser4Shaughnessy,Dunne3Tanser
Henderson6Power16 Erhahon7McGrath
1 Alnwick.
Substituted for Offord at 81 minutes.
22Fraser.
Booked at 52 minutes.
18Dunne
3Tanser
12Henderson
6 power.
It was 69 minutes.
Substituted forKiltieat 74' minutes.
Substituted for Dennis at 56 minutes.
Substitutes.
11Kiltie
15Reid.
20Dennis.
23Erwin.
There are 26 lies.
33Offord.
44Millar
The Rangers and St. Mirren match ended in a draw.
The second half ended with Rangers winning.
Joe Aribo won a free kick.
Alan Power had a foul.
The attempt was saved. The shot from the centre of the box by Alfredo Morelos was saved in the bottom right corner. James Tavernier assisted with a through ball.
The Rangers' Alfredo Morelos won a free kick.
Foul by Charles Dunne.
The substitution was for St. Mirren. Ryan Flynn was replaced by Kieran Offord.
An attempt was missed. Scott Arfield missed his shot from the left side of the box. They were assisted by Alfredo Morelos.
An attempt was missed. The shot from the centre of the box misses to the right. Scott Wright assisted with a cross.
The substitution was for St. Mirren. Jamie McGrath was replaced by Greg Kiltie.
Corner, Rangers. Scott Tanser was Conceded.
The attempt was blocked. Fashion Sakala's shot from a difficult angle on the right is blocked. Scott Arfield assisted.
The attempt was saved. James Tavernier's shot was saved in the bottom right corner. Borna Barisic had a cross.
Corner, Rangers. Conceded by Jamie.
The yellow card for a bad foul is shown to the young man.
James Tavernier won the free kick.
Foul by Erhahon.
The Rangers had a substitution. Ianis Hagi was replaced by Fashion Sakala.
The Rangers had a substitution. Ryan Kent was replaced by Scott Arfield.
