JACK ROSS has described how he will be looking for Sunderland to keep an eye on their discipline after a crushing 3-0 defeat at Peterborough United that has left his squad “sore.”

Despite expressing an intention to appeal against Luke O’Nien’s straight red card for an incident with Ivan Toney with 19 minutes remaining at London Road with his side already trailing by three, he still thinks his players have to be mindful of their actions.

Striker Charlie Wyke was dismissed six minutes later for his second bookable offence when he lunged in to Posh full-back Dan Butler, with Ross also questioning some of referee Craig Hicks’ other decisions.

The Sunderland manager said: “First of all, as a general thing, our discipline has been good this season but we do have to remind ourselves of that because last season there was a stage where it cost us points. Today didn’t cost us points (already behind) but it did have an impact on how the game panned out. That is the learning curve for us.

“I don’t think Luke’s was a red card. I have seen it only once since, I will have to see it again. I think Charlie is two cautions. He has to make good decisions when he is already on a yellow.

“However, there was a large degree of inconsistency in what it took to get a caution in the game. I am fair in saying that and balanced.

“I have no complaints on the two yellows he got but there were an awful lot that went unpunished. The sheer inconsistency in what was required to get a yellow was baffling at times.

“My first thought is we will appeal Luke’s. He swings round but it was a grapple, it’s not a punch and not worthy of the reaction. I will speak to the officials and go from there.”

The cards aside, though, Ross was disappointed with the outcome when he felt Sunderland, looking for a sixth straight win, had looked capable of winning until Peterborough scored the second six minutes into the second half.

“It is a sore one for us,” he said. “There are days when you need to take your medicine and deal with it. We ae disappointed. It is sore but it is a long season and we have opportunities to put a run together and forget about this.

“It is strange standing here because people will have a perception of how the game went after that scoreline. We did well first half against a good team away from home, I thought we looked solid defensively and a threat going forward.

“The free-kick (from Marcus Maddison) aside we would have been relatively happy at half-time. We still believed we would win the game after that as well. We were on the ascendancy and after that things happened in the game that made it nigh on impossible to win the game.”

Ross revealed Denver Hume missed out because of an ankle injury, while Chris Maguire failed to recover from a knock. Sunderland hope to sign a new left-back on Monday.

On an afternoon when Sunderland struggled to test goalkeeper Christy Pym, the Black Cats’ huge band of away supporters at London Road were subjected to a dreadful collapse.

Peterborough were already three goals up when Sunderland had O’Nien and Wyke sent off within the space of six second half minutes as frustrations boiled over.

County Durham-born Sunderland fan Marcus Maddison did most of the damage for Posh.

The man who the Wearsiders decided was not worth £2.5m in the summer - after a chat between the two clubs - fired Peterborough in front with a brilliant 25-yard free-kick in the 36th minute.

He also added the third in the 64th minute when he started and finished a move after receiving the ball back from George Boyd deep in the Sunderland half.

In between those, and six minutes after the break when Sunderland pushed for an equaliser, Peterborough broke and added a second.

Mo Eisa made the most of the space down the left-hand side and, after an interchange of passes on the edge of the visitors’ box, Josh Knight was picked out unmarked and he drilled low inside Jon McLaughlin’s far corner.

Then Sunderland saw red. O’Nien was dismissed for an off the ball incident with Toney with 19 minutes remaining before soon after Wyke, who had already been cautioned, dived into Butler to receive his red. The only blessing was those didn’t lead to more goals.

PETERBOROUGH UNITED (4-3-1-2): Pym; Mason (Thompson 84), Beevers, Kent, Butler; Knight (Burrows 80), Reed, Boyd; Maddison; Eisa (Dembele 63), Toney. Subs (not used): O’Malley, Bennett, Tasdemir, Ward.

SUNDERLAND (4-2-3-1): J McLaughlin; O'Nien, Ozturk, Willis, C McLaughlin; Leadbitter, Power; Gooch (Grigg 63), McNulty (Flanagan 74), McGeady (Dobson 78); Wyke. Subs: Burge (gk), McGeouch, Baldwin, Embleton