Both players are 8-under 134 after Singh shot 7-under 64 and Howell shot 3-under 68 in Friday's second round.
Singh, who has won three majors, reached 5-under for the championship with an eagle at the ninth hole.
"I made an eagle on No. 9 that really relaxed me and just gave me a really good mood to play relaxed golf on the back nine," Singh said.
First-round leader Adam Scott (72), Brett Quigley (66), Luke Donald (65), Frank Lickliter (67), Ben Crane (66), Kevin Sutherland (67), Arron Oberholser (69) and Geoff Ogilvy (68) are tied for sixth at 5-under 137.