Martin Braithwaite tucked past Bristol City keeper Niki Maenpaa to open the scoring
Middlesbrough's unbeaten start to the season continued with victory at Ashton Gate against an uninspiring, injury-hit Bristol City side.
Tony Pulis' visitors took advantage of some poor Robins defending early on as Martin Braithwaite applied a simple finish to grab his third goal of the season.
Britt Assombalonga's header from Stewart Downing's dinked cross doubled the lead before half-time.
Winless Bristol City saw far more of the ball but failed to turn their greater share of possession into clear chances.
The closest Lee Johnson's side came to a goal was when Eros Pisano headed against the crossbar late on, as they lost at home for the second time in four days after Tuesday's shock Carabao Cup exit at home to Plymouth.
Centre-back Aden Flint, who switched from Bristol City to Boro for a reported fee of about £7m in June, was facing his old side for the first time after five seasons at Ashton Gate.
The impact of the sale of the 6ft 6in talisman on the Robins' defence had been exacerbated by injuries to four of the club's defensive options, with Nathan Baker, Bailey Wright, Taylor Moore and Jens Hegeler all out.
And hesitation at the back led to the opening goal for in-form Denmark striker Braithwaite's opener, as Boro made it three wins and a draw from their first four league games of the season, while the Robins have two points from three Championship matches.
Bristol City boss Lee Johnson told BBC Radio Bristol:
"I think I should apologise to the fans for our first half performance. It was soft and disappointing because we knew about the physical attributes of our opponents.
"We huffed and puffed and tried to blow their house down. Their house was made of brick and ours was made of paper... as it proved for the first goal.
"If you get brushed aside like we did for that first goal, it's always an uphill battle - particularly against a Tony Pulis side with good resources for the division."
Middlesbrough boss Tony Pulis told BBC Tees:
"We were strong. Our two centre-halves, [Dael] Fry and [Aden] Flint, look a good pair. We were pretty dominant. They've still got to do certain things I'm not pleased about, but they gave us a solid base.
"The five in midfield again worked really, really hard. Stewart [Downing] was always a threat down the right-hand side and Martin [Braithwaite] really could have had another two.
"Our quality in the changeover of play has got to be better, because there were chances or opportunities to play people in and we missed those chances because we didn't see them or the pass wasn't very good."
