But John-Joe O'Toole got forward to head home a Lee Brown free-kick after 84 minutes for Rovers and ensure the spoils were shared.
Lewis said: "We looked pretty comfortable for most of the game and had good chances to increase the lead, so I'm disappointed in that respect.
"James hadn't scored for a few games but we know he is a quality finisher and he got on the end of a very good move.
"We should have seen the game out but we started giving away too many free-kicks and putting ourselves under pressure.
"Even so, a point away at Bristol Rovers is still pleasing because they have some very good players and an excellent manager."