An early own goal from Stevie Hammell and a late headed second from William Gros gave Kilmarnock a win and three points that they scarcely deserved.
And Nicholl - standing in for Kenny Shiels who was serving a touchline ban - was honest in his assessment after his side took the win despite being pounded by Motherwell.
"We had a great start to the game and although we were lucky to get the own goal I thought here we go," said Nicholl.
"Then we did nothing except face waves of attacks from Motherwell when we just couldn't get the ball out of our own half.
"I said to the players at half-time that they didn't have a hope in hell of winning the game if they continued like that - and I'm sure they were sitting in the Motherwell dressing room wondering how they were 1-0 down at half-time, and I was asking how we were 1-0 ahead."
Gros popped up on his own goal line three times to produce clearances, denying Shaun Hutchison and also after keeper Lyle Letheren had palmed a Simon Ramsden header onto the bar.
But Motherwell failed to maintain that first half pressure and Gros grabbed the all important second goal, nodding a James Dayton cross past Darren Randolph to make it a more comfortable final 20 minutes for the home side.
Any worries of a late fightback from the visitors disappeared when red cards for Fraser Kerr and then captain Keith Lasley in the final six minutes reduced Well to nine men.
That disappointed manager Stuart McCall who was also left frustrated after his team failed to turn their chances into goals.
After dominating most of the first half and not scoring the Well boss lamented missed chances.
He said: "If it was a boxing match it would have been stopped at half-time but credit Kilmarnock for the numerous blocks on the line.
"I thought we were rusty in the first 10 minutes but dominated the half hour after they scored but just couldn't put the ball in the net - but that's what is all about."
McCall said of the two red cards: "I am not happy as we lost our discipline.
"Fraser Kerr has had a swipe at the ball and caught the player and Keith Lasley's challenge was born out of frustration but it is not acceptable."
Dayton, the victim of the two challenges which resulted in the red cards, did not think there was any malice in what led to the dismissals.
He said: "I took a bit of a whack both times but I don't mind as it is part of the game.
"I wasn't being targeted or showboating but I suppose having ridden our luck in the first half their players were a bit frustrated after being denied so many chances and just lost their discipline."