Republic of Ireland striker Scott Hogan scored a brace to earn Birmingham side a thumping 5-0 win at Luton.
Blues led after seven minutes when Roberts beat Elijah Adebayo to a corner and powered his header beyond Simon Sluga.
Luton fell further behind after 26 minutes as the hosts could not clear their lines and Tahith Chong's cross met by Hogan, who cleverly directed his header into the net.
Two minutes into the second half and it was 3-0 as Birmingham broke at pace. Although Pelly-Ruddock Mpanzu managed to get back and make a covering tackle, the ball ran through to Hogan who had the easiest job of tapping into the empty net for his second of the afternoon.
Gary Gardner added a fourth on 85 minutes, arrowing into the top corner with virtually his first touch and minutes later Chuks Aneke rounded off the scoring.
Fulham moved to the top of the Championship after beating Hull 2-0 at Craven Cottage.
Aleksandar Mitrovic and Fabio Carvalho, as they had done against Millwall in midweek, scored first-half goals as Marco Silva's side leapfrogged West Brom on goal difference.
West Brom won 2-1 at Blackburn to also make it 10 points from four games.
Alex Mowatt and Matt Phillips scored at either end of the first half at Ewood Park to put Albion in control.
Chile striker Ben Brereton Diaz pulled one back for Rovers with his fifth goal in seven games, but the Baggies held on for another victory.
Stoke are third after beating Nottingham Forest 1-0 with a Josh Tymon goal and Coventry continued their progress by climbing to fourth with a 2-1 win over Reading.
Substitute Matty Godden grabbed a winner eight minutes into added time to seal a dramatic comeback win for the Sky Blues.
John Swift’s first-half penalty had put the Royals ahead before Jamie Allen equalised after 62 minutes.
QPR fought back to draw 2-2 at home to Barnsley with Charlie Austin grabbing a stoppage-time equaliser.
Barnsley led 2-0 through first-half goals from Dominik Frieser and Cauley Woodrow – his 50th for the Tykes – before Ilias Chair halved the deficit 14 minutes from time.
Cardiff complete the top-six after defender Aden Flint scored two for the second successive game.
The Bluebirds beat Millwall 3-1 with Flint’s fellow centre-back Sean Morrison also on target seven minutes from time.
Benik Afobe had given the Lions hope after 76 minutes, six minutes after Flint completed his second-half brace.
Blackpool fought back to draw 2-2 at Bournemouth after Dominic Solanke had scored twice for the Cherries inside 19 minutes.
A rare James Husband goal and a Jerry Yates penalty gave the Seasiders a deserved point.
Huddersfield claimed a dramatic 2-1 Yorkshire derby win against Sheffield United at Bramall Lane.
Levi Colwill’s winner came in the fourth minute of added time, just moments after Billy Sharp had cancelled out an earlier effort from Josh Koroma.
The Blades have yet to win under new boss Slavisa Jokanovic and are one place off the foot of the table.
Forest, who have lost their first four games, are the only team below Sheffield United.
Preston picked up their first points of the season by beating Peterborough 1-0 at Deepdale.
Patrick Bauer scored the only goal after 14 minutes, while Wayne Rooney saw his Derby side held 0-0 at Pride Park by Neil Warnock’s Middlesbrough.