Kyle Walker-Peters opened the scoring but goals from Milutin Osmajic and Brad Potts put the home side back ahead after the break.
It took Gavin Bazunu going up for a corner in the final seconds of six minutes added on for his aerial contest to force Ched Evans to put through his own net.
It secured a 2-2 draw for Saints, who are now unbeaten in five Championship matches with three wins in that time.
Speaking to the Daily Echo after the match, Martin said: “The first 30 minutes were really good, really controlled. But either side of half-time has cost us.
“At the end of the first half, we conceded way too many set pieces because we weren’t brave enough to play. A couple of kicks long which we hadn’t done the whole game.
“We then carried that on into the second half and that wasn’t the message at half-time, so it’s the most frustrating thing in the world.
“We wobbled a little bit but even after a scare or whatever, you need to stick to the plan and the detail. In games where we have been 1-0 up, we haven’t shown enough to really turn the screw.
“We will learn through that and we had to make a lot of changes, so I am delighted with a point, although we didn’t make enough of the moments we had.”
Martin made five changes from his team that beat Hull City with a last-second goal on Saturday, citing fitness concerns in the squad.
He revealed: “Three or four changes were enforced and one was about energy and from speaking to the players about how they feel.
“We wanted to learn from the last three-game week and Rotherham. Wee Man (Ryan Fraser) was due to play but had to pull out due to a virus.
“Kamaldeen picked up a bit of an injury against Rotherham, before the international break, so we kept that under wraps but it’s been about managing him this week.”
Martin continued: “I am really pleased with the point as we have a chance now on Saturday to make it a brilliant week.
“I felt we gave away too many set-pieces because we weren’t good enough on the ball and we didn’t deal well enough with the atmosphere or momentum