Roberts, a January signing from Blackburn Rovers, scored his third goal in four matches as Brian McDermott's side recorded a fourth consecutive win.
Southampton regained the lead in the Championship after thumping Derby County 4-0 on Saturday.Hosts Southampton led 1-0 by half-time at St Mary's Stadium thanks to Jos Hooiveld's 14th-minute goal.
Aaron Martin and Adam Lallana scored in the space on nine minutes early in the second half to blow the lead out to 3-0.
And Tadanari Lee capped off the rout when he netted in the 75th minute.
Leeds came from 2-0 down to win 3-2 at home to Doncaster Rovers, thanks to a 90th-minute winner from Luciano Becchio.
Trailing to two goals either side of half-time from Mamadou Bagayoko, first Andros Townsend and then Adam Clayton scored to draw Leeds level.
Becchio then netted a dramatic winner following a lengthy injury delay, with newly appointed manager Neil Warnock watching from the stands.
Elsewhere, Chris Martin claimed a brace as Crystal Palace saw off Watford 4-0 at home.
James O'Brien and Matt Done were on target in the second half as Barnsley recorded a 2-0 victory over 10-man Portsmouth.
Two Lee Martin goals and one from Michael Chopra helped Ipswich Town beat Cardiff City 3-0 at home.
Lee Tomlin also scored twice as Peterborough United dispatched Bristol City by the same scoreline, with David Ball claiming the other goal.
Finally, Nottingham Forest recorded their first victory from seven matches in all competitions, as they defeated fellow strugglers Coventry City 2-0 at home.
