Pep Guardiola has seen it all before. The Catalan coach led Barcelona to the greatest era in the club's history with Lionel Messi at the forefront of his superb side between 2008 and 2012. But he created a monster - and now it keeps coming back to haunt him.

During his tenure at Camp Nou, Guardiola always admitted that Messi made the difference. "Without him, we would be competitive," he often said. "But we wouldn't have achieved all that we have."

However, he had played his part in the Argentine's astronomical rise to become the world's finest footballer. Before Pep's arrival as coach in 2008, Messi was fantastic yet fragile, mesmerising but also inconsistent. And his best return in front of goal was 17 over a single season.

In 2008-09, that changed dramatically. Messi looked fitter, faster and hungrier in a spectacular season in which he helped Barca to the treble and netted 38 goals along the way. "I play closer to the area now," he would say. But it was much more than that. Pep paid attention to every detail of Leo's game - and made him the best player in the world.

Four consecutive Ballons d'Or followed for the Argentine and, more importantly for Barcelona, an astonishing 14 trophies out of 19 in the Guardiola era before the Catalan coach left to take a sabbatical in 2012.

Pep then returned to Camp Nou to watch Barca against City as Bayern Munich boss in March 2015, witnessing a Messi masterclass from the stands and covering his eyes in disbelief when the Argentine nutmegged James Milner. "It is a luxury to watch Leo," he said afterwards.

Asked about stopping his former forward ahead of Bayern's clash against Barca later on in the same season in the Champions League, Guardiola was blunt. "There is no defence that can stop him," he said. "It's impossible. He is used to players defending against him any way they can and he always ends up enjoying success. He is too good."

That proved to be the case again as Messi hit two sensational strikes in a 3-0 win for Barca in the first leg of the semi-final between the two sides at Camp Nou, the first a fierce drive from outside the box to break the deadlock and the second a clever chip over Manuel Neuer from a tight angle after he had left Jerome Boateng grounded.

This time, though, City made a real game of it in the first half and had chances to hurt Barca. But again, Guardiola was powerless to resist Messi, who rounded Claudio Bravo to score the first after Fernandinho had slipped, brilliantly culminating a move he himself had started outside the area with Andres Iniesta.

And after Bravo was sent off for a ridiculous handball outside the box, it was Messi - who else? - that further punished Pep and City. The five-time Ballon d'Or winner lashed home from long range to make it 2-0 and completed his hat-trick from much closer in after Ilkay Gundogan gifted the ball to Luis Suarez. Later, he also won a penalty and let Neymar take the spot-kick, the Brazilian missing before adding a fourth in an ultimately one-sided victory.

That is twice Pep has returned to Camp Nou as a visiting coach now, and the stats make difficult reading for the 45-year-old: no wins, no draws and no goals in two defeats, with seven conceded, five of those scored by the world's best player.