Hamilton was topped only by Ferrari's Fernando Alonso in first practice on Friday, before setting a day-best lap of one minute 47.490 seconds in the afternoon session.
The Brit, who trails team-mate Nico Rosberg by 22 points in the drivers' championship with six races remaining, said being on pole was important heading into Sunday.
Four of the past five Singapore GPs have been won by the polesitter, including Hamilton's win in 2009.
"Today was a work in progress. We made some changes between P1 and P2 and, whether it was those changes or the track itself, the balance didn't feel right," Hamilton said.
"It felt like we lost a bit of performance but we'll look into the details and see what it was tonight.
"The long run was okay - I had a bit of traffic which wasn't ideal, as when you back off to rebuild the gap the tyres come back to you a bit which may not give an accurate picture of exactly how long they will last. Pole here has always been very important.
"The right side of the grid, for example, always seems to get the better starts.
"Being up at the front will be crucial and that's obviously my target for qualifying tomorrow.
"Nico looks very quick, as do the Ferraris and the Red Bulls, but I'm feeling good this weekend and I'm focused on the job."
Rosberg was third in the opening session of the Asian F1 swing, but was halted on a hot lap in the afternoon when Lotus' Pastor Maldonado crashed on turn 10.
The German said it was the only glitch of the day, as he looks to build on his championship lead.
"I had a good feeling in the car. The only pity was that I had to abandon my quick lap due to the red flags," he said.
"Although I didn't get the second part of that lap, though, in the first part the car felt great.
"We then decided to do more laps on high fuel to learn more for the race and overall it was okay.
"It will be difficult with tyre degradation on the softer tyre so we still need to work on that.
"But it's generally a great challenge driving here."