Geoff Horsfield fired Wigan into a fifth-minute lead and missed a chance to double the Latics' lead early in the second half.
The Blades made the most of their escape when substitute Lester fired home a spectacular equaliser.
Wigan had opened the scoring in their first real attack of the game, and it was a wonderfully created opportunity down the right channel.
Nathan Ellington lofted a sublime pass over the defence for Andy Liddell to chase and a pinpoint cross found Horsfield just six yards out and he really could not miss.
Wigan's Tony Dinning was extremely fortunate to escape a caution for a wild lunge at a grounded Paul Peschisolido, although Mike Whitlow could have few complaints for the yellow card he received for a crude challenge on the live-wire Jimmy Bullard shortly after.
Michael Brown tested Latics goalkeeper John Filan with a couple of long-range efforts before fizzing a teasing cross across goal that Ashley Ward came desperately close to converting.
At the other end Liddell tried his luck from distance but Paul Gerrard held on with Horsfield ready to pounce while Lee McCulloch drilled over without troubling the keeper before heading over from Nicky Eaden cross.
Horsfield almost made in 2-0 within seven minutes of the restart but his acrobatic volley from a Liddell cross fell just wide.
There were half-hearted calls for a Blades penalty midway through the second half when Chris Morgan went down under very little contact but the referee was unimpressed and waved play on.
Liddell threatened with 15 minutes remaining when he cut in from the right, beating three men on the way, but McCulloch could only shoot tamely and the chance had gone.
The Blades continued to push without creating a clear-cut chance until substitute Lester, on for Stuart McCall, cut in from the left and smashed an unstoppable shot past Filan.