LIVERPOOL, England -- No defeat is easy to take -- especially when it is the first of the season -- but if Manchester City are to enjoy the greatest campaign in the club's history, Pep Guardiola and his players may come to regard the day they lost 4-3 at Liverpool as the most important result of them all.

Some perspective is required at the end of City's 30-game unbeaten Premier League run. Ahead of Manchester United's Old Trafford encounter with Stoke City on Monday, the leaders remain 15 points clear at the top of table.

Put another way, that's so far ahead of the chasing pack that Guardiola's men could lose four more games and still remain on top. If United don't beat Stoke, City could lose five times and, more than likely, retain top spot on goal difference.

The Etihad Stadium club have one foot in the Carabao Cup final following Tuesday's 2-1 semifinal first-leg victory over Bristol City, they face a lower league opponent -- either Cardiff City or Mansfield Town -- in the FA Cup fourth round and their pairing with FC Basel in the Champions League Round of 16 is as close to a free pass into the quarterfinals as they could wish to have.

But the loss to Liverpool saw their aura of invincibility evaporate and that will give Premier League rivals some hope of masterminding their own wins against the leaders. It would be foolish, naïve and arrogant to dismiss Sunday's result as nothing more than a bump in the road and, in Guardiola, City possess a manager who will not allow it to pass without a thorough post-mortem.

Liverpool exposed deficiencies that need to be resolved if they are to progress on all four fronts. Domestically, City remain way out in front but, if that continues to be the case, the biggest concern for their manager will be what happens in the latter rounds of the Champions League.

Winning a domestic treble would be a historic achievement, but it would feel like a hollow one if City failed to deliver in Europe's biggest competition. With Real Madrid in turmoil and Bayern Munich in transition under Jupp Heynckes, only Barcelona and Paris Saint-Germain would appear to pose a significant threat.

However, all four of those Champions League heavyweights will look at the video of the defeat at Anfield, pinpoint the problems currently being experienced by City and realise that they can exploit them.

Pep Guardiola has plenty to ponder but Manchester City have no need to panic. Peter Byrne/PA Images via Getty Images

Up-front, Sergio Aguero appears short on sharpness and confidence, while injury to Gabriel Jesus has blunted City's edge. If, as is expected, they miss out on Alexis Sanchez to Man United, the solution that Guardiola had identified will not available.

Raheem Sterling, Leroy Sane, Kevin De Bruyne and the two Silvas -- David and Bernardo -- are all capable of making up for any shortage of goals from the strikers, though, and Guardiola will be confident that his side can to outscore most opponents, even if Sanchez does move to Old Trafford.

It is in defence where the most attention needs to be paid and this defeat against Liverpool will enable Guardiola to go back to the drawing board. Jurgen Klopp's forward players forced defenders into numerous mistakes, many of which were costly: Three of Liverpool's goals came following errors by John Stones, Nicolas Otamendi and goalkeeper Ederson respectively.

The ongoing absence of the injured Vincent Kompany does not help City and Guardiola, nor does the lengthy injury layoff for left-back Benjamin Mendy. His replacement, Fabian Delph, limped off in the first half at Anfield with a knee injury that Guardiola claimed would keep him out "for a while."

When City have players missing at the back, the likes of Danilo and Eliaquim Mangala are not good enough to plug the gaps, so those areas are ripe for improvement. Crystal Palace and Bristol City have both found frailties in City's backline in recent weeks, but Liverpool blew a hole in them.

If complacency had set in, losing in this fashion will be a wake-up call. Guardiola admitted after the game that the number of fixtures facing City in the second half of the season will be a drain on their resources, which has prompted his search for reinforcements. Defensively, they certainly need at least one new signing and, more than Sanchez, that must now be the priority.