Two-time Australian Open champion Chalmers kept his errors to a minimum with just two bogeys on the Harbor Shores course in Michigan that gave so many fits on Saturday.
Four-time major champion Els also minimised mistakes and hit wedge in tight for birdie on his final hole for a 69 and a share of the lead.
Left-hander Chalmers and Els were at 10-under 203, with LIV Golf player Richard Bland of England one shot back, having led at 12 under before posting a 74.
Australians were featuring strongly with Richard Green tied sixth and two shots from the lead after a 70 while Scott Hend (70) was a further shot back at seven under and Cameron Percy (68) was four under.
Chalmers ran off five straight birdies starting on No. 6 to take the lead before his golf got a "little scratchy" on the back nine.
It was the control of irons that left him thinking he has a good chance to capture his first senior major.
"Not super comfortable with my driver today, but I was very comfortable with every other area of my game," Chalmers said.
"So if I can just get that squared away for tomorrow, see if we can get out there and compete. Looks pretty bunched up at the moment, so should be an exciting day, hopefully."
Els too is looking for his first senior major title.
"I'm fortunate enough to be up there," Els said. "You know, 10 under is leading at the moment; 12 under was leading yesterday. I played solid. I didn't play spectacular, but played solid enough to get myself up there."
There was enough wind, difficult pin positions and tough greens on the Jack Nicklaus design that it took nearly six hours for the 83 players who made the cut to complete the third round.
"Hopefully, we can move better tomorrow," Els said.
There could be a lot of movement on the leaderboard. Harbor Shores yielded its share of birdies, particularly on the par 5s that were downwind, but it didn't take much for players to get out of position and find themselves scrambling for par.
Even so, it was crowded at the top.
Bland and Chris DiMarco, who didn't make a birdie on the back nine in his round of 71, were one shot behind. Richard Green of Australia had two eagles and still only managed a 70 after a bogey on the final hole.
The four players who were three shots behind included defending champion Steve Stricker, former British Open champion Stewart Cink and Jason Caron, a former PGA Tour player and one of the club pros competing in the Senior PGA Championship.
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