On the back of his impressive display last weekend – scoring the solitary goal against Birmingham City – the attacker continued with the form sealing the victory at Ashton Gate.
The DR Congo international headed home Stewy Downing’s cross in the 32nd minute of the game after Martin Braithwaite had opened the scoring for Tony Pulis’ men.
The former Nottingham Forest player was replaced by Ashley Fletcher with one minute left on regular time.
The victory ensures that Middlesbrough maintain their four-game unbeaten run as they continue their domination on the league table with ten points.
Assombalonga will be looking to continue with the imposing form when Middlesbrough trade tackle with West Bromwich Albion on Friday.