Motherwell manager Stephen Robinson hailed his "ruthless" side after they claimed a 4-0 Ladbrokes Premiership victory over St Johnstone at Fir Park.

Robinson had demanded exactly that attribute after feeling they had let slip the opportunity to take something from last weekend's 2-1 defeat by Hibernian.

Devante Cole headed the opener after a quiet first quarter and Peter Hartley and Jake Carroll netted following second-half corners in between a decent period from the visitors.

Christy Manzinga came off the bench to net a debut goal in an 89th-minute counter-attack as Motherwell made the most of their five shots on target – the other was a header from Hartley which was cleared off the line.

Robinson said: "It was the complete opposite of what we had last weekend.

"This week we were ruthless when the opportunities arose for us and some of the defending was very, very good when it needed to be.

"Jake Carroll's header at the end and Mark O'Hara's header at the end, determined to get a clean sheet. That's what wins you football matches.

"It's a strange game because we have played a lot better than that. We were a little bit flat. I thought the whole day was flat, the crowd was flat, we were flat, there is bit of an illness going about the squad and we weren't our best but we still controlled the game.

"Speaking to the boys after, a few of them felt a wee bit under the weather. I think you could see that with our sharpness and some of our decision making.

"Maybe the 4-0 scoreline flattered us a wee bit but we were always in control of the game. But we can be better than that."

St Johnstone manager Tommy Wright admitted he needed an experienced defender after his side lost their 33rd goal of the Premiership campaign.

Wright said: "I counted seven decent balls in our box, and three of their goals came from seven crosses.

"We started the game quite well but the game is all about what you do in both boxes and we didn't do enough.

"We had a four versus two at 0-0 and our best chance of the game at 2-0 when Matty (Kennedy) has a great chance to put us back in it.

"But you can't defend like that and I can't defend it because it's individual errors that cost us.

"I see Hartley at the end of the game, probably one of the only good crosses we put in, putting his body and head on the line.

"My players can do it but they don't do it consistently enough. Motherwell will not get four easier goals all season.

"It's frustrating but until we get some experience in the team, they are just going to have to deal with it.

"I have to be patient with them and stick with them because that's what we have got until January.

"We will get an experienced defender in. We possibly could have got one a month ago but that didn't happen."

Wright added that defender Wallace Duffy had only jarred his knee after going down under no pressure and would likely be fit for Wednesday's trip to Kilmarnock.