In a scrappy contest on Teeside, the Swans failed to get out of second gear as two goals from Emmanuel Latte-Lath proved to be the difference on a difficult afternoon for the away side.
Latte Lath, a summer signing from Atalanta, moved into double figures for league goals this season with strikes either side of half-time as Boro extended their unbeaten run to seven games.
Swansea travelled to the north-east having lost their last three away league matches at the Riverside Stadium. Another defeat means now they are still looking over their shoulders in the Championship with the gap just five points between the bottom three with six games remaining.
Following sluggish performances over the bank holiday weekend against Sheffield Wednesday and Queens Park Rangers, Williams called for a rise in performance against Boro.
What the former Notts County boss would get, however, would be one lacking conviction, desire and intent.
“The way we played today was unacceptable,” said a clearly angered Williams after the match.
“It was completely unacceptable; it was lacking in energy and conviction. We conceded two ridiculous goals, we showed nowhere near enough for our supporters to watch that and be happy with what they saw.
“We had nothing. We got players into unmarked positions in the box, the number of times we got close and overhit a cross or made a bad touch. It’s just sloppiness, there is not enough focus or concentration.
“We did not turn up. Think of the supporters who have travelled up here, excited to come and see their side in this stadium and we produce that. It’s brutal.
“This is a big football club; we are one division away from the Premier League. We cannot play football like that again, what would be the point of that?
“We have to be better than that in the games ahead, it better be blood and thunder.”
The Swans now move on to face Stoke City at the Swansea.com Stadium on Wednesday night before welcoming rock-bottom Rotherham United to south Wales on Saturday afternoon.
[Lead image: Swansea City]
