Ghana captain Andre Ayew was on the scorescheet and also provided an assist as his side Swansea City defeated Luton Town 2 nil in the Championship.
The win sent the Swans into the Championship play off spot after overcoming Wednesday's defeat their third this season against Middlesbrough.
But the smile returned to the Swansea head coach's face as they extended their unbeaten home run to five matches.
Luton will feel hard done by having created enough opportunities to get back into the game after Swansea went ahead in the second minute through Roberts' deflected shot.
But Swansea just did enough to hold on to their lead before Ayew's low drive sealed a third win in their last five matches.
Luton lost defender Matty Pearson 21 minutes from time when he was shown a second yellow card.
They drop a place to 12th in the table, while Swansea are two points from top spot in fourth.
Swansea have been hard to beat at home so far this season, while Luton have impressed on their travels since Nathan Jones returned to the club for a second spell as manager in May.
They were well beaten just along the motorway at Cardiff City last Saturday, yet Jones' side have banked 20 points from their 11 away fixtures before this.
Their hopes of further improving that fine record got off to a dreadful start as Swansea scored from the first attack of the game.
Korey Smith, Liam Cullen and Ayew were all involved in a sharp passing move before Roberts' left-footed shot sailed into the Luton net with the aid of a significant deflection.
Swansea continued to apply pressure, with Ben Cabango heading Roberts' free-kick straight at goalkeeper James Shea before Cullen pulled a shot wide.
But the visitors eventually found their feet, pressing Swansea high and forcing them into errors in possession.
Luton almost levelled when George Moncur's 25-yard curler was pushed on to the post by Freddie Woodman, and they really ought to have equalised when Ayew's loose ball handed Jordan Clark possession deep in Swansea territory.
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