After ending a seven-game winless run against Bolton Wanderers on Tuesday, the Smoggies continued with the impressive form at the Riverside Stadium with the Congo DR international playing a key role in the tie.
The 26-year-old striker scored the solitary goal in the 25th minute to take his tally to 11 this season and help his side clinch their 17th win this term.
Assombalonga was on parade for the full duration of the encounter along with Nigeria international John Obi Mikel who made his 14th league appearance in the tie.
The victory saw the Smoggies move closer to promotion play-off spot as they climbed to the seventh spot having gathered 64 points from 42 games.
Assombalonga will hope to deliver another impactful performance when Middlesbrough host Stoke City on Friday.