A John Terry own goal gave Swansea an unexpected lead, but Costa was imperious as he found the net three times to maintain the Stamford Bridge club's 100 per cent start to the Premier League season.
Debutant Loic Remy added a fourth after coming on for Costa, before Jonjo Shelvey netted a late consolation for Swansea.
Costa has now scored seven goals in four Premier League matches, but Mourinho does not expect his close-season acquisition from Atletico Madrid to continue at the same rate.
"Seven goals in four Premier League matches is maybe too much," he said. "We cannot expect that after eight matches he has 14 goals. I think it's asking too much.
"But the way he 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.
"Seven goals in four matches has surprised me because it is something that is not normal.
"You cannot repeat it in a cyclic way - four matches, seven goals, four matches, seven goals. Maybe in the next four matches he'll score two goals.
"But he's comfortable in the team. The team was built in a way where we were waiting for a certain type of striker and I think now everybody knows that Chelsea did the right thing by waiting for him and not going to the market in the summer of 2013 or January 2014 just to buy a striker."
"Chelsea did well by waiting for the right one."
Asked if there were similarities between Costa and Chelsea legend Didier Drogba, Mourinho added: "Didier had a fantastic career at Chelsea and Diego is showing that he can have the same profile of career."
The result saw Chelsea move clear at the top of the Premier League, while a 2-2 draw between title rivals Manchester City and Arsenal also played into their hands.
However, Mourinho insists he is only interested in his own team's performances at this stage of the season.
"For me, there is no context," he stressed. "At the moment it is about playing.
"You cannot go into mathematics now. Mathematics is when there are 10 matches to go and how many points you need to finish first, second or in the Champions League.
"At the moment it is just about playing and trying to get the maximum possible points."
