The triumph under the roof at Steaua Bucharest was Chelsea's second away win of the season, following the Capital One Cup success at Swindon.
The Blues will target a third on Sunday at Norwich in the Barclays Premier League and Mata is confident of further improvement from the team.
"I'm sure the best is still to come from the team," he said.
"We have a good young squad and we have signed young players this season. We will get even better in the future.
"The last few games have been good and we are building momentum. I think it's normal that we needed time (to adapt to the new manager), but we are doing that.
"Now we have to keep going and take advantage of this victory, to keep winning."
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