ESPN has it as:
Fábregas 09/10
PL: 27 appearances, 15 goals, 13 assists
CL: 7 appearances, 4 goals, 2 assists
FA Cup: 1 appearance, 1 assist
Mata 12/13
PL: 35 appearances, 12 goals, 12 assists
CL: 6 appearances, 3 goals, 3 assists
FA Cup: 5 appearance, 1 goal, 5 assists
I reckon the heights Mata reached last year are being greatly overstated more than anything, personally. Mainly because there's a lack of genuinely top players in the league compared to when Fábregas was here (and previous to that). Or people are just looking at Mata's sensational numbers and remembering a few quality goals and judging him off of that alone. All three of his goals in the CL came against Nordsjælland, as did two of his three assists (in a meaningless 5-1 win), and then there's things like assists against a United side with Scott Wooton in it or against midtable Championship sides. It's only worth comparing league and Champions League records, really. In any case he played 65 games for Chelsea last season and got a goal or assist in just over half of them (34). Impressive but hardly mindblowing.
Fábregas had the better numbers in 09/10 no matter what stat site you use and he's obviously more influential in the build-up so to me it's clear he's had a better season and is the better player. Better final ball, better finisher and more influential in the build-up.