The Blues were stunned 0-2 by Aston Villa on Sunday.

The result left Chelsea in fourth spot on 10 points - the same number as leaders Liverpool, but the Reds have a game in hand.

The only consolation for Chelsea supporters, perhaps, is that they are still two points ahead of champions Manchester United.

It was only Chelsea's second loss in 32 league matches.

While Mourinho was disappointed with the result, he should not have been surprised.

After all, he admitted that the competition is much stiffer this season.

He told The Telegraph: 'In my opinion, there are lots of good teams in the league.

'I think it can be more normal that the big teams lose games and points because the other teams spend money.

'They bought players, they changed their teams, they improved their team.

'Villa are one example, but you can find a lot of other examples in the league.

'So I think it is more difficult to play against these teams, because they are better teams.

'Probably because of that, the league is open.

'Anyway, it is the first weekend of September, five matches in the Premier League, it means nothing.'

Of the top four in the Premier League, only Everton are a surprise inclusion - with Liverpool on top, Arsenal second and Chelsea in fourth.

So it is unlikely that Mourinho will be hitting the panic button.

The surprise loss - Villa have not beaten a team from the top four in four years - was a timely reality check for the manager.

Goals by debutant Zat Knight and Daniel Agbonlahor earned Villa the victory, and denied Chelsea the chance to return to the top.

The Blues lacked a cutting edge, and paid the penalty. Poor defending at a set-piece allowed Knight to score a 47th-minute header from Gareth Barry's corner, reported football365.com.

Said Mourinho: 'Aston Villa played well, Chelsea played well and, in my opinion, a point each would have been a fair result.

'But Chelsea made a mistake you cannot make. We are very organised in defence at set-pieces.

'But a game we were in control of, after a solid first half, changed with that goal early in the second half.

'After that, Villa were well organised, showed great spirit and had the crowd behind them.

'The second goal means nothing. That can happen sometimes in the last couple of minutes, when you are pushing forward.

'I accept the result but I don't think it's fair. But Villa did not make the sort of mistake we made.'

Villa manager Martin O'Neill believes the result will give his players the belief that they can compete with the big guns.

He has spent more than £40million (S$122.7million) on revamping his squad since American owner Randy Lerner's buy-out 12 months ago.

O'Neill said: 'Chelsea were brilliant in defeat, but I'm absolutely delighted with our efforts.

'We had to play with a lot of determination and belief, and I think we did that.'