Jose Mourinho believes Diego Costa's scintillating start to his Chelsea career proves he was right to wait for the Spain striker.

Costa returned from a hamstring injury sustained on international duty to score a hat-trick in the Blues' 4-2 Premier League victory over Swansea at Stamford Bridge on Saturday.

And with Costa already now up to seven goals from his four opening matches, Chelsea manager Mourinho is delighted with the £32 million ($53.1 million, 40.4 million euros) striker, who only arrived in the close-season even though the west Londoners have been searching for a forward since last year.

Costa's contribution against Swansea left Chelsea as the only team to have taken maximum points from their four league games this season.

Chelsea now face Schalke at home in the Champions League on Wednesday with Mourinho hoping Costa provides a similar performance, although he is eager not to put too much pressure on the 25-year-old.

"If the team plays well he has to score goals," Mourinho said. "Seven goals in four Premier League matches is maybe too much, we cannot expect that after eight matches he has 14 goals.

"I think it is too much to ask but the way he is playing and the team is playing, if he keeps scoring a few goals, a few goals give points and points help the team to be in the top part of the table.

"He surprises me because seven goals in four matches is something that is not normal.

"But he's comfortable in the team and the team is built in a way that we were waiting for a certain type of striker.

"And I think everyone knows Chelsea did the right thing by waiting for him and not going to the market in the summer of 2013 or January of 2014 just to buy a striker."

Swansea went ahead when Chelsea captain John Terry diverted Neil Taylor's left-wing cross into his own net on 11 minutes.

It was a lead Swansea merited, but Costa equalised from a Cesc Fabregas corner just before half-time.

He then added a further two goals at 11-minute intervals by side-footing in from Fabregas and Ramires passes before he was replaced by French striker Loic Remy, who then went on to sweep in a debut goal from the edge of the area.

On Remy's cameo, Mourinho added: "It's a perfect debut. He scored on his debut at Stamford Bridge in a goal that is special at this stadium because there are no away fans behind it."

Swansea still had time to restore a measure of respectability to the scoreline that their first-half performance had merited when Jonjo Shelvey reduced their arrears four minutes from the end.

It was a reality check for Swansea boss Garry Monk after the three successive wins which had brought his Manager of the Month award for August.

"I said it before the game; I think they'll be there or thereabout and I think they'll be champions," Monk said of Chelsea.

"The whole team is packed with world class players that can cause damage to you at any time and that's obviously why they pay the money that they pay to get the players."

Chelsea now look ahead to Wednesday's Champions League tie and Mourinho is wary of the opposition that lie in wait, with Schalke, Maribor and Sporting Lisbon making up their group.

"The group is more difficult than people think," Mourinho said. It's not because I'm Portuguese but the Portuguese teams are very difficult.

"The Germans are the Germans and Schalke improved a lot in relation to the last season. Our group is difficult, it's hard.

"We also have fixtures that are lot a poison gift for us because every time we play in the Champions League, the next match we play is against Manchester City, against Arsenal, against Manchester United and against Liverpool."