Indeed it was fitting that Gros claimed the second which eased the home nerves as the Killie forward was responsible for three goal-line clearances as the visitors bombarded Kyle Letheren's goal in the first half.
But Motherwell's frustrations got the better of them in the closing minutes when firstly Fraser Kerr and then captain Keith Lasley were shown straight red cards for wild tackles on James Dayton.
Following a pretty even start Kilmarnock took the lead after 12 minutes. Ross Barbour out wide on the right drilled a low ball into the box only for Stevie Hammell's outstretched leg to deflect the ball past his own goalkeeper from 10 yards.
That should have given the home side a platform to build on but instead Motherwell took the game to their opponents with style and pace.
A series of crosses and corners from both flanks had the Killie defence stretched for the remainder of the half with only a host of goal-line clearances keeping the home side in front.
Keeper Lethernen had to thank Gros, who popped up on the goal-line on 24 minutes to clear Shaun Hutchison's powerful header.
Remarkably it took another clearance from the Killie forward on the half hour to deny Hutchison with a thumping volley eight yards in front of a packed goal.
Then from yet another Tom Hateley corner Simon Ramsden's header was palmed on to the face of the bar by Letheren, leaving Gros to once again clear the ball out of the six-yard box.
Kilmarnock continued to be on the back foot after the break.
The introduction of Garry Hay for Borja Perez almost had an immediate impact when the experienced full-back curled a shot from the edge of the box over Randolph's bar.
After 69 minutes 'Well brought on Kallum Higginbotham for his first appearance but it was the home side that doubled their lead two minutes later when Gros headed in James Dayton's inviting cross.
Motherwell were then reduced to 10 men six minutes from time. Fraser Kerr, having replaced Hateley only four minutes previously, was first to go for a wild swing at Dayton. And three minutes later Lasley followed him into the dressing room following a similar challenge on Dayton as Killie comfortable held on to their lead.