Wednesday night, however, was anything but a happy return.
Lionel Messi's 37th Barcelona hat-trick set the Catalan side on its way to a comprehensive four-goal win, leaving Guardiola with plenty to ponder ahead of the return fixture in November.
An evening to forget was compounded by a horror error from Claudio Bravo, resulting in the goalkeeper being sent off -- although Barcelona also finished with 10 men after Mathieu saw red.
"We paid for our mistakes," Guardiola told British broadcaster BT Sport. "At this level it's hard. Until it was 10 against 11, the game was open and we competed against a very good team.
"We created enough chances to score a goal but after that (red card) the game was over. I spoke with Bravo, he is disappointed but he won't change.
"He's one of the best goalkeepers of the last 10 years. Mistakes happen, he is sad but will learn a lot."
The opening stages didn't progress as Luis Enrique and the Catalonia faithful had perhaps anticipated.
After Neymar comfortably waltzed past Nolito and centered a cross to send an early warning sign to the City defence, it was the away side which dominated.
The rather unusual sight of Messi somewhat desperately clearing the ball long up-field after a period of sustained City pressure epitomized the match's opening minutes.
It then got worse for Barcelona's under pressure defense, as left back Jordi Alba was forced off with an injury and replaced by Frenchman Lucas Digne.
But, in typical Barcelona fashion, its first chance led to a first goal -- albeit thanks to a huge slice of luck on the way.
Messi collected a loose ball in midfield and drove towards the penalty area, before playing a ball into Neymar.
The Brazilian's return pass looked to be misplaced and harmless, but Fernandinho's slip at the worst possible moment allowed Messi to latch onto the ball and dance around Bravo to tap into an empty net.
That set the atmosphere alight on what had been an otherwise subdued evening inside the Nou Camp, thanks largely to City's early dominance.
Not willing to let their heads drop, City almost levelled soon after. Ilkay Gundogan delicately evaded challenges from Gerard Pique and Javier Mascherano, before a brilliant, low save from Marc-Andre ter Stegen denied him a glorious goal.
Barcelona was dealt a further blow as Pique limped off injured to be replaced by Jeremy Mathieu, with the home side now without half of its original starting defense.
Just seconds before the end of the first half, David Silva's tantalizing cross into the box found John Stones completely unmarked four yards from goal, but he somehow contrived to head the ball wide of Ter Stegen's post.
City certainly didn't deserve to be behind at the break and Guardiola's tactics stifled the fearsome triumvirate of Messi, Luis Suarez and Neymar expertly, highlighted by the fact MSN were the three players who completed the fewest passes in the first half.
As the second half commenced, both teams struggled to gain the upper hand -- until Bravo used his outside of the penalty area to get sent off.
The Chilean keeper came rushing out of his area to meet Ivan Rakitic's through ball and, despite getting there well ahead of Suarez, Bravo's miskick went straight to the Uruguayan's feet.
Suarez's chipped shot was palmed away by Bravo, who was several meters outside of his area, leaving referee Milorad Mazic no choice but to send him off.
Messi put the subsequent free-kick harmlessly over the crossbar, but it wouldn't be long before he got his second.
Kevin De Bruyne's loose pass gifted the ball to Andres Iniesta, who found Messi on the edge of the area to drill into the bottom corner.
It was looking like a long night for City and the task at hand became even more daunting thanks to a Gael Clichy error.
The Frenchman's errant pass found Suarez, who unselfishly set up Messi to poke the ball into the net for his hat-trick.
Three mistakes from City, three goals for Barcelona.
The visiting side looked to be handed a reprieve when Mathieu was shown a red card for two yellows within the space of three minutes.
But it could have been even worse for City, as Aleksander Kolarov fouled Messi in the penalty area. The Argentine elected to give the spot kick to Neymar but a hesitant, stuttering run up was followed by a poor strike and Bravo's replacement Willy Caballero saved comfortably.
Just minutes later, though, the Brazilian had his goal. Receiving the ball from Messi, Neymar went past Stones and this time found the bottom corner.
"I'm quite tired and thank goodness there is only one Pep," Luis Enrique said in his press conference. "If there were five of him it would be a lot more difficult. So I am going to sleep.
"This is what we expect from Messi. His days of inactivity make no difference, it is total interpretation of football. He never stops surprising us with the things he does, he helps the team with everything."
'A German Team'
From FC Midtjylland to FK Vojvodina, there are often unfamiliar European clubs that leave football fans feeling tongue-tied.
Sometimes, they're just plain "Odd
" (in the case of a Norwegian team).
But one German club with a particularly long name came up with a novel way of making life easier for watching fans, after taking inspiration from a British pub.
Borussia Monchengladbach decided to take heed from one sign writer who clearly had trouble spelling its name, ahead of Wednesday's Champions League clash with Scottish team Celtic in Glasgow.
Instead of the 23-letter tongue-twister, the club -- often called simply "Gladbach" -- has opted to change its name on Twitter to a more palatable "A German Team."
For all the pre-game jesting, the match was actually a crucial one for both teams. With Barcelona and Manchester City the other two clubs in Group C, points in this fixture are all the more precious.
And if Celtic fans had trouble saying Borussia Monchengladbach before Wednesday's fixture, they won't be forgetting it in a hurry now.
Second half goals from Lars Stindl and Andre Hahn gave 'A German Team' a comfortable win, the first time the club has kept two consecutive clean sheets under coach Andre Schubert.
Barcelona sits top of the group, five points clear of Manchester City in second. Borussia Monchengladbach are now just a point behind, with Celtic languishing in last on one point.
Six of the best for Ludogorets
While Messi was getting his 37th Barcelona hat-trick, Mesut Ozil hit the first of his career.
The German playmaker, more often used to providing assists than finding the back of the net, helped Arsene Wenger register his 100th victory in European competition with a win over Ludogorets.
Alexis Sanchez's delightful chip got the home side off the mark just after 10 minutes, before Theo Walcott and Alex Oxlade-Chamberlain got in on the act.
Ozil's second-half treble added gloss to the scoreline for an imperious Arsenal side that is now unbeaten in 11 matches, winning nine of them.
"It was good to watch, because they were dangerous as well," Wenger said after the match. "But the second half was a bit more one-way traffic, but it's good because we continue to score goals and today as well we didn't concede.
"It was a positive night for us. Confidence is of course stronger with every win," the Frenchman said, referring to his side's seven game winning streak.
"So we have to keep our vigilance and confidence and bring that into the next game."
With Paris Saint-Germain defeating Basel, Arsenal remains top of group A on goal difference with qualification to the round of 16 almost sewn up.