Jose Mourinho is predicting the Barclays Premier League title race will be more open this season after seeing Aston Villa end Chelsea's 18-game unbeaten run.

Goals from debutant Zat Knight and Gabriel Agbonlahor earned Villa a 2-0 win which denied Chelsea the chance to return to top spot.

It was their first league defeat since losing to Liverpool at Anfield in January.

But Mourinho feels the money spent this summer by Villa and other sides outside of the top four will mean more surprise results could happen in the next nine months.

The Chelsea boss said: "There has been a big input by teams outside of the top four so it will become more normal for the big teams to lose matches and points.

"The other teams have spent lots of money and brought players in to bolster their teams. Villa are one example but you can find a lot of other examples

"It will be more difficult to play against these teams because they are better. The league is open but it is the first weekend of September and we are only five matches into the season."

Chelsea dominated for long periods but lacked a cutting edge and paid the penalty when poor defending at a set piece allowed Knight to score a 47th-minute header from Gareth Barry's corner.

Mourinho said: "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 that 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 to me in the context of the game. That can happen sometimes in the last couple of minutes when you are pushing forward.

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

Chelsea owner Roman Abramovich left the directors' box immediately after Agbonlahor had wrapped up the points in the 88th minute when he converted a cross from Ashley Young.

But Mourinho played down the significance of this action. He said: "I think the owner leaves the stadium when he wants to leave. I went to see England-Germany the other day and I left early because I wanted to beat the traffic."

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

O'Neill has spent more than £40million on revamping his squad since Randy Lerner took charge of Villa 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.

"Chelsea are the sort of side that can score a goal in an instant and I was pleased to hear the final whistle but when we had the ball we caused them problems.

"We have a bit to go yet but that result and performance is really encouraging. We needed a result like that to give the players belief that they can play and perform against the big sides."

O'Neill was delighted with the performance of Young who has earned his first England call-up for the forthcoming games with Israel and Russia.

He said: "We have some fine talent and Young was sensational. When he picks the ball up the crowd are waiting for something to happen now.

"He ended last season really well, played well for the England Under-21s in the summer and has carried that form on.

"But we have a lot of pace in our side now which can cause the opposition plenty of problems."