The Spaniard's half-time introduction against Tottenham saw the Blues leave White Hart Lane with a point on Saturday, with the manager rewarding him with an 81-minute run out against Steaua Bucharest on Tuesday.
Mata has spent much of this season out of Mourinho's starting line-up but, after featuring in three games on the trot, he expects his contribution to increase.
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"I try to improve every season, my first and second seasons were fantastic but I want this one to be even better so I will try to improve, score goals, assist and do what I have to do."
Chelsea were dominant against Steaua, winning 4-0 to banish the memories of their shock home defeat to Basel two weeks ago, and Mata feels the result will give the squad impetus.
"I think after the defeat against Basel, which was a painful defeat, we needed to win," Mata added. "From the first minute you could see we wanted to win.
"We scored twice in the first half and another two in the second half, I think we played really well and it's going to be better in the future because this result gives us confidence."
Schurrle, meanwhile, echoed his team-mate's sentiments, before commenting on his own chances of secure a more regular first-team berth.
The German said: "It was very important, we lost the first game against Basel and this was a must-win game. We created chances and scored four goals which was very important.
"We played with confidence and were always looking to finish. It was a deserved win, 4-0 was a good result because we scored goals but I think we could have scored more.
"I always want to start and to play, the manager knows that. It's good for me that I started and I hope I played well, but the most important thing was to get the three points because we needed them, that's all that counts.
"I try to give my best on the pitch and show my qualities, that's all I can do."