Goals from Jim Goodwin and Lewis Guy bagged all three points for the Saints as they made it nine points from their first six games in the SPL this term.
It has been an impressive start from the Paisley side and Lennon was full of praise for his players after a deserved triumph.
He said: "All week we spoke about it being a test for us as we hadn't beaten Hearts. We always just fell short, but always had good performances. We made a conscious decision about what it was going to take mentally to get the three points and I thought we did it fantastically well. We passed that test, but unfortunately for us we now have 31 more tests.
"Hearts got out of the traps very well. They're a very big team and I felt we handled that admirably. We then got our-selves in front with a wonderful strike from Jim Goodwin.
"I felt that with Hearts opening up we were able to counter attack them and we looked in control of the game. I'm not going to say we were in control of the game in terms of possession, but mentally I felt we were very comfortable and that is a great testimony to the players.
"Make no mistake about it Hearts are a good side and we could easily have found our-selves trailing early on in the game, but there was some won-derful defending by us and Craig Samson's not really had any real one-on-one saves to make.
"The international break gave us some time to reflect on the opening games of the season – we've done okay but there's a big test from us. There's one or two things we're delighted in, one or two we're not and we're working hard to make things right."
The points were all but secured for the Buddies when Guy netted just after the break, converting from close range after good work from Steven Thompson. And Lennon was delighted with the showing of his strike duo.
He said: "I thought Steven was exceptional from start to finish both in possession and out of possession. It was a real team performance. Lewis is so quick, he gets support in there and plays off the shoulder and big Stevie had that option."