MANCHESTER, England -- Three thoughts from the Etihad Stadium on Manchester City's 2-1 win over Liverpool in the Premier League.

1. Sane, Aguero finally snap Liverpool's unbeaten start

Leroy Sane's 71st-minute winner for Manchester City reignited the Premier League title race and ended Liverpool's unbeaten start to the campaign, as the champions moved to within four points of the leaders with a vital 2-1 victory at the Etihad.

Having taken a first-half lead through Sergio Aguero's stunning 41st-minute thunderbolt, City were pegged back on 64 minutes when Roberto Firmino headed in from close range after being teed up by Andy Robertson.

Jurgen Klopp's team, who had not been beaten in the Premier League for 242 days, almost took the lead in the first half when City defender John Stones produced a crucial goalline clearance after his initial attempt to clear had hit goalkeeper Ederson.

City survived that scare to take the lead through Aguero, but Liverpool had been the better team in the first half; the home team struggling to recapture the form that saw them win the league by a 19-point margin last season.

Firmino's equaliser, followed by Sane's winner, capped a pulsating second half, but City's win denied Liverpool the chance to open up a 10-point gap by claiming victory. Four points is still an impressive lead for Liverpool, who remain favourites to win the club's first league title since 1990.

Liverpool's aura of invincibility has now been shattered, though, and the question now is all about how they respond, especially as they are the hunted this season. City simply have to keep the pressure on and hope they get some help from their rivals against Liverpool.

Man City needed a win to pull within striking distance of Liverpool and while it wasn't always pretty they got it Thursday at the Etihad. Getty

2. Man City need to tighten up at the back

Manchester City have kept the title race alive by beating Liverpool, but the champions will not be able to sustain their challenge unless they tighten up defensively.

It is now 11 games in all competitions since City kept a clean sheet -- the 4-0 win at West Ham in November -- and this game once again highlighted their issues at the back. Fernandinho was immense in central midfield and helped paper over some cracks but the defence remains an issue and that was obvious here.

Injuries to key personnel is one major factor, with Benjamin Mendy missed at left-back and his replacement, Fabian Delph, missing due to suspension. With both players absent, Guardiola deployed Aymeric Laporte at left-back and the Frenchman never looked comfortable away from his usual centre-back spot.

But Pep Guardiola caused that problem for himself by dropping Kyle Walker to the bench again and forcing Danilo to play at right-back. Had Walker been selected, Danilo could have slotted in at left-back and the impressive defensive pairing of Laporte and John Stones could have remained intact in the middle.

Vincent Kompany, for so long a reliable servant at the back, was starting back-to-back league games for the first time since August and his ring-rust showed. The Belgian was fortunate not to be sent off for a dangerous lunge at Mohamed Salah in the first half, with the City captain escaping with a booking and eventually came off limping ahead of the final whistle.

Walker's loss of form, Mendy's injury and Kompany's fading powers have left City vulnerable at the back, but they need to find a way to get back to their best defensively.

If they don't Liverpool should overcome this blip and coast to the title.

Danilo's struggles vs. Liverpool again highlighted Man City's current predicament at full-back. Photo by Matt McNulty - Manchester City/Man City via Getty Images

3. Salah goes missing again vs. a top-six rival

This was a game when Liverpool needed Mohamed Salah to produce a moment of magic to maintain their unbeaten run, but the Egyptian forward once more had a no-show against one of the Premier League's big guns.

He still has a respectable 16 goals in 28 appearances in all competitions this season, but he has now played against City twice and failed to trouble the champions' defence, Minus producing one good save late from Ederson, Salah was notably quiet here, missing a big chance to give Liverpool a stranglehold on he title race.

Salah has also fired blanks against Tottenham, Chelsea and Manchester United this season, and one goal in two games against Arsenal is all he has to show for his appearances against the top-six this campaign.

One factor in Jose Mourinho's decision not to hand Salah regular football at Chelsea was his belief that the player did not affect the big games. Salah debunked that theory last season by providing the goals that fired Liverpool to the Champions League final, but if he has been missing one thing in his game this term, it has been his ability to hurt his team's biggest rivals.

Not only did Salah fail to score at the Etihad, he also did little to contribute away from the penalty area. Salah is a great player and one reason why Liverpool are still top of the league, but he needs to raise his game against the big clubs if Liverpool are to stay there.