Boro boss Tony Pulis blamed Boro's slow start for the defeat to Sheffield United on Tuesday evening.
"The first half was very disappointing on all fronts. I thought we started so slow and so sloppy," he said.
"They score a good goal, top corner, volley from the edge of the box, which knocks us back.
"The sending off, this is a game of challenges and Grant's not gone in with his studs up. He's made a challenge and the kid's a bit quicker than him, but it's disappointing.
"His first booking was silly, you accept that, but people are making these challenges honestly.
"The second goal is another disappointment, from a cross. We're down to ten men and we've got a situation where people have to take responsbility with who we're marking."
Pulis made all three substitutions at the midway point, and although he was pleased with the second half reaction, remains frustrated to be leaving empty-handed.
"I thought the three subs really livened the game up for us. They brought us energy and real commitment," he said.
"Britt - that's as well as he's played for me - and he really gave us something up front.
"Clayts did really well in the middle, and Fabio, who has just come back, his energy and commitment set things off.
"We really took the game to them second half and we're disappointed not to come away with anything.
"If we'd played with the same enthusiasm in the first half, we'd be here talking about a victory."