Chelsea's Branislav Ivanovic has noted that Manchester United's stellar start to the Premier League season doesn't guarantee lasting success.
The Red Devils have won all four of their matches so far this season, accruing 18 goals.
Ivanovic admitted that while this is impressive, Chelsea had a similar start to last season but failed to win the title.
"United started very well this season but, if you remember, we started last season the same," explained the 27-year-old.
The Blues, currently two points behind United, will travel to Old Trafford on Sunday to face the team that caused their exit from the Champions League in April.
"They've improved as a group but we have our aim, we have our idea and we try to use this on the pitch," the defender added.
"It's going to be the hardest game for us until now and we have to show more than 100% of our power.
"We can go also on the top after this game. Psychologically for both teams, it's a very important game."
A win could place the visitors at the top of the table with 13 points.
Dan Saney
