Filip Helander was left cursing the late lapse that dented Rangers' Ibrox clean sheet record, leaving their hopes of breaking Chelsea's British defensive record hanging in the balance.
The unbeaten champions have won all 17 games at home, keeping 14 clean sheets in the process, with Motherwell's Callum Lang and Dundee United striker Marc McNulty the only other two players to net at Ibrox.
In total, Gers have now shipped just 11 goals in 34 games.
Chelsea set the British record for goals conceded when they let in just 15 in the 2004-05 campaign as Jose Mourinho took the Premier League by storm in his first campaign in English football.
Rangers remain on course to beat that benchmark as they also close in on an invincible league season with four games remaining.
But Helander was frustrated by the late slip which allowed Nisbet to glance home as the Light Blues saw their wriggle room reduced.
The Swede told RangersTV: "I think we controlled the game good in the first half and then started off quite well in the second half and got to 2-0.
"Then we conceded a goal and obviously that makes it harder. They get some energy and we had to really fight for it, but it was a victory and we have got to be happy with that.
"Of course it was hard to take (to lose a goal). We fight so hard to get that (clean sheet) and we didn't.
"We are disappointed with that of course, but when you win that is obviously most important. Our victory record here at Ibrox is nice.
"Most of the game we did well, but when you concede a goal you can't be too happy about it.
"It is something that we have got to look at what happened there."
Gerrard will hope his defence will be watertight when they take on Celtic later this week in the last 16 of the Scottish Cup.
Helander added: "Of course it is a big game (against Celtic). There is one more title to get so we are looking forward to it.
"We have got to prepare well for it and hopefully we will get a good result there."