O’Nien has been pushed back up the pitch after an excellent stint at right-back, but missed out on a starting place as George Honeyman returned from injury.
As he has done all season, he came off the bench to add tenacity and drive to the Black Cats.
“Luke’s really good performances have come out of position,” Ross said.
“I think it was important to get Adam [Matthews] back in that area because he’s the best full-back we have at the club, in terms of that [right back] area.
“It was between George [Honeyman] and Luke as to who was going to play in that [attacking midfield] role and you could have made a good argument for either of them. George has been a miss for us because he brings a whole load of different things to the game.
“The good thing with those two in particular is if they both play or one of them plays, you know what you will get from them every single time and they both showed that. When Luke came off the bench he made a good contribution off the bench as well.”
That was not the only big selection call Ross had to make.
Chris Maguire was due to miss out on the squad entirely until Lynden Gooch had to withdraw from the side late on.
“There will be tough decisions every single week now but that’s the way it should be,” Ross said.
“It means there’s no hiding place in training.
“The players have trained well all season but when you’ve not got really strong numbers there’s not a lot you can do with it. Now we’ve got that real strength in depth and competition for places we can.
“There were a few different choices to make and will continue to be for the rest of the season but it just means the players have to train well to give themselves a chance to be in the squad and if they play well they will stay in the team.”
Ross also praised Grant Leadbitter for making a quick impression on Wearside.
Leadbitter completed 90 minutes and laid on an assist for Aiden Mcgeady’s winning goal.
The Black Cats boss says his contributions off the pitch are already as important.
“I’ve been really impressed with him in training,” he said.
“He’s a great addition for us in terms of the way he is around the club – I’ve got a few of them in Lee [Cattermole], Glenn [Loovens] and George, who make a good contribution people don’t see. Grant is part of that.
“He’s not played in this league before, so even that was new for him. I mean that in the best possible way because it is different. You could see it a couple of times where he had people snapping at his heels and maybe you don’t get that [in the Championship], but he adjusts to it because he’s a clever player and he played a part in the goal.
“He did well to last the 90 minutes and he had to dig that out mentally as well because he’s not played a lot this season.
“He’s got a good understanding of the game, good experience within the game, and that willingness to share it. Not all players are comfortable doing that.
“He’s that type. I’ve seen it in training and he’s only been here a couple of days.
“I think he’ll still be a little bit within himself because he’s getting familiar with the group and each individual character,” he added.
“The more types you’ve got like that, the better, because it helps you see out difficult games like Saturday’s, and win them.
“I’m really pleased for him. It was emotional for him.
“Football’s very peculiar nowadays and we’ve become very cynical and mercenary but that was emotional for him. It was a big deal for him coming back here to play. I think he wanted to get through the early period of the game and settle into it.
“He’ll be glad that’s out the way now and he feels as if he’s properly started his Sunderland career again.”