MK Dons were denied a third-straight victory after Jonathan Obika's 90th-minute goal earned Swindon Town a share of the spoils at The County Ground.
They were then made to rue those missed opportunities, as in the 90th minute Obika pounced on a defensive mistake and slotted past Nicholls, forcing Robbie Neilson's men to settle for a point.
The Dons boss made two changes to the side who beat Charlton Athletic in midweek, with George Williams returning at the heart of the defence in place of Paul Downing. Agard also came into the starting XI, with Robbie Muirhead making way.
Swindon, fighting for their lives at the bottom of Sky Bet League One, came into the game on the back of successive victories over promotion-hopefuls Millwall and Fleetwood Town, and they made a strong start in front of their home fans at The County Ground.
It was the Robins who had the first chance on 10 minutes - a header from Raphael Rossi-Branco which sailed over Lee Nicholls’ crossbar.
The Dons responded two minutes later but Ben Reeves couldn’t get a clean connection on Harvey Barnes’ cut-back.
Barnes was one of two scorers in the midweek win over Charlton, the other being Stuart O’Keefe, and the on-loan midfielder went close to adding to his goal tally on the quarter-hour mark when he rattled the frame of the goal with a drive from 20-yards out.
That chance was followed after by an effort from Agard which was dealt with by Lawrence Vigouroux, as the Dons began to turn up the heat on their Wiltshire opponents.
Neilson’s side remained the team in control thereafter, limiting their hosts to very few openings and looking dangerous on the attack.
They almost capped their dominance with an excellent team goal in the 38th minute but Reeves wasn’t able to find a way past Vigouroux after some superb football from Ed Upson and O’Keefe.
Reeves went close again less than two minutes later - the number 10 with one his trademark left-footed curlers which, this time, didn’t dip enough to nestle in the top corner.
Just when it looked like the Dons would be forced to settle for a stalemate at the break, they were presented with a golden opportunity to take the lead.
The impressive Reeves got goal-side of Charlie Colkett in the box before being bundled over by the Swindon midfielder.
Referee Graham Salisbury pointed straight to the penalty spot and that allowed Agard the chance to extend his goal tally for the season to 14 - the 27-year-old duly obliged, finding the bottom left-hand corner with his spot-kick to give his side a deserved half-time advantage.
The Dons went in search of doubling their lead right at the start of the second period, earning a corner after just 30 seconds but it was directly from that set-piece, where Swindon went agonisingly close to drawing level.
Reeves’ corner was cleared away by the Robins, who countered with Goddard. The midfielder carried the ball deep into the Dons’ penalty area but was denied by an excellent save from Lee Nicholls.
Saturday’s game was another chance for Nicholls to impress between the sticks and while he could take credit for the save from Goddard, he had the post to thank for keeping out Jon Obika moments later - the striker climbed well to meet Colkett’s cross but hit the wrong side of the woodwork with his header.
With 10 minutes gone in the second period, Neilson switched things about, moving to a back five with Paul Downing entering the field in place of Ben Reeves, with the aim to counter Swindon’s own change in formation.
While the switch may have appeared defensive, it did lead to a period of sustained pressure on the Swindon goal.
First, Barnes hit the post after beating his man inside the penalty area and then Upson threatened with a bullet of a half-volley which went just wide of the post.
The midfielder went even closer when he crashed a curling shot against crossbar on 71 minutes before Muirhead was denied an easy tap-in by a sliding Nathan Thompson.
Neilson’s men would have been wondering how they weren’t two goals up after the latter of those openings but there was little time to ponder as the Robins began throwing men forward in search of a late leveller.
Substitute Ben Gladden cleared the crossbar with an effort from 20-yards while Obika did the same with an acrobatic effort on 76 minutes.
Swindon's came close again with two minutes remaining but Williams came to the Dons' rescue, getting in the way of the close-range effort and keeping it out of Nicholls' goal.
The Robins, though, were able to find a late goal - Obika the man to get it, slotting past Nicholls after pouncing on a defensive mistake.
Obika's goal came in the 90th minute but there was still time for both sides to have further chances on goal.
The best opportunity fell Upson's way with six minutes of added time played but the midfielder wasn't able to convert after being picked out in the area by O'Keefe.
Starting XI: Nicholls; Baldock, Williams, Walsh, Lewington (c); Upson, Potter, O’Keefe; Reeves (Downing 56), Agard (Muirhead 64), Barnes (Brittain 89).
Unused subs: Martin (GK), Tilney, Thomas-Asante, Bowditch.
Goal: Agard (pen 43)
Booked: Walsh, Lewington
Attendance: 7,946 (589 away)