Manchester City returned to the top of the league after comfortably seeing off defending champions Chelsea 3-0 at the Etihad Stadium.Sergio Aguero opened the scoring after a bit of a personal battle with Blues stopper Asmir Begovic, finally scoring on his fifth attempt at goal inside the opening 30 minutes.Chelsea struggled to react positively and couldn't find a way past City's resilient defence, despite enjoying a fair bit of possession. John Terry was hauled off by Jose Mourinho at half-time, much to the surprise of the world and his wife, but City came out strongly in the second half and dictated the rest of the game.Vincent Kompany headed in the second before Fernandinho finished things off with a wonderful first time drive to send the Etihad Stadium in to raptures.As title deciders go, this was pretty clear cut. Chelsea are well off the pace at the very start of their title defence, while City already look like they could be the team to win it this year.So here's three things we learned from this afternoon's crunch clash at the Etihad...

John Terry's legs have gone

John Terry

He's been at the heart of Chelsea's defence for well over a decade, but it certainly looks as if John Terry's Chelsea career is on its last legs.

The 34-year-old was hauled off by Mourinho at half-time as the Blues struggled to handle Manchester City's attacking force - Terry's legs had quite clearly gone.

Terry played every minute of every game for the Blues last season, but it appears another consistent season for him is a bit too much to ask...

Man City are definitely the team to beat

Manchester City v Chelsea - Barclays Premier League

Everyone had Chelsea down as the team to beat before a ball was even kicked this season, but after just two games the tables have well and truly turned.

Man City were extremely impressive in their 3-0 mauling of West Brom on Monday night, but to follow that up with a 3-0 mauling of the defending champions is even more impressive.

Manuel Pellegrini's men were absolutely superb from start to finish and deserved all three points against a Chelsea side that simply didn't look like title contenders.

They're now five points clear of Chelsea after just two games - Manchester City's title bid is well and truly up and running. Chelsea have so much to do if they want to defend their crown.

While the likes of Man United, Arsenal, Liverpool and Chelsea are yet to show anything that even remotely looks like title challenging form, City are turning on the style.

Mourinho needs to strengthen

It's not rocket science - you can't stand still while your closest title rivals spend money and strengthen.

So far that's exactly what Chelsea have done and, if Jose Mourinho doesn't thrown some money at improvements before the end of this summer's transfer window then you fear for what will come of Chelsea's season.

They struggled last week at home to Swansea and were then humiliated at Manchester City today. They're five points behind league leaders City and don't look anywhere near a side capable of winning the league.

He arguably needs a striker, a centre-half and another midfielder, or he can kiss goodbye to back-to-back titles.