The fitness of Manchester City's Sergio Aguero could decide the outcome of the Premier League title race.The Argentinian scored a brilliant goal and made another as Manchester City swept past Norwich City in the FA Cup third round at Carrow Road, and if he can remain injury-free for the rest of the campaign, the Blues chances of earning silverware are increased greatly.Manager Manuel Pellegrinis side, complete with five Argentinian players in the starting lineup, won 3-0, a result that keeps their hopes of an unprecedented quadruple alive.But it was Aguero's performance that was perhaps the most pleasing aspect for City fans. He has spent much of the season either injured or recovering from a lay off, but there are now clear signs hes returning to his very best.His goal was remarkable. He collected a neat flick into his path from Raheem Sterling and took on three defenders with a mazy run before prodding the ball into the bottom corner with minimum fuss.And on the half-hour mark, he set up Kelechi Iheanacho for his fifth of the season, bringing a long ball under instant control before advancing into the area and slipping in to the 19-year-old Nigerian, who finished despite having little room to engineer a shot.Aguero tweeted: "Good win to get us into the fourth round of the FA Cup and be a contender in every tourney. C'mon, City!Iheanacho is now averaging a goal every 75 minutes this season and has to be firmly in Pellegrinis first-team plans for the remainder of the campaign.Aguero and Iheanacho were full of pace and movement at Carrow Road. It was sharp, inventive link-up playthe kind City have lacked for much of the season.Aguero has seldom been match fit; Iheanachos opportunities have been limited.Wilfried Bony, the clubs 25m signing, fails to offer anything like the dynamism those two are capable of. The Ivorians lack of movement has often appeared at odds with Pellegrinis open, attacking philosophy, stifling the sides best moments.Iheanacho will surely leapfrog him in the pecking order.The City boss said afterward that he feels Aguero is key to his side producing their best.The goal that he scored demonstrated hes 100% fit, said the Chilean.But you can be 100% in fitness, and if you dont have the quality of Sergio, you cannot score that goal.He demonstrates in every game that he is improving.When you have important players like Sergio, it is important for the team-mates, for the manager, for the fans to see him playing every game because hes a player that makes the difference.Sergio scored a beautiful goalits not the first time hes done it.We all know how good he is. Hes just coming from injury.We need to keep his performance and try to be fit to the end of the season.Nicolas Otamendi tweeted: "Gran victoria equipoa seguir por este caminoGreat Victory of the team to go trough to the next round."Kevin De Bruyne added Citys thirdhis 11thgoal of the campaign alreadyand Jesus Navas, once again, demonstrated his value with a display full of pace and intent.The Spanish winger had become something of a target for disgruntled fans earlier in the season after some lackluster performances, but in recent weeks his qualities have often been used to give City added impetus from the bench.He deserved his start on Saturday and showed again that the width and pace he offers give City an extra dynamic.As FA Cup wins go, this was about as perfect as youre going to see. City rotated their side, brought in some players who needed minutes, dominated from the off, scored three goals and were in total control throughout the match. Not once was their place in Round 4 under any threat.Pellegrinis side have shown inconsistency this season, but they are still in four competitions and have everything to play for during the second half of the campaign.Their star striker being fully fit and firing makes them a far more formidable outfit.Rob Pollard is Bleacher Report's lead Manchester City correspondent and will be following the club from a Manchester base throughout the 2015/16 season. All quotes were obtained firsthand unless otherwise noted. Follow him on Twitter @RobPollard_. Click here to read full news..