The Briton sits 11 points behind team-mate Nico Rosberg and initially on Friday it looked as though it was gearing up to be another dominant weekend for the German.
The championship leader topped the timesheets in first practice with Hamilton edged out into second by 0.097 seconds.
However, it was the 2008 world champion who finished with the fastest time as Hamilton staked his claim at Spa-Francorchamps.
"It's great to be back in the car and it was feeling good out there today," said Hamilton. "The morning wasn't as strong, but it definitely improved in the afternoon.
"As always, we still have work to do tonight, but overall today was okay."
Meanwhile, Rosberg was pleased with his performances and expects the Mercedes to perform well despite the demands of the track affecting downforce.
"Today went according to plan," he told ESPN.
"It's difficult here because to be quick here you have to run less downforce to be quick on the straights, which means our car is sliding more in the corners and that means it's more difficult to drive and a bit unusual.
"It takes a bit of adapting and finding the right set up, but all-in-all we are going in the right direction."