The Lions were 4-0 victors at the New Den, with goals from Kevin Lisbie and Liam Trotter combining with two goals from Steve Morison. Poor defending from the Tigers contributed substantially to their loss.
That leaves the London side as one of only two Championship teams to win both their games.
Neil Warnock returned to haunt his former side Sheffield United, as Queens Park Rangers ran riot at Bramall Lane.
The R's scored all their goals in the first 23 minutes, with Ephraim, Jon Mackie and Adel Taarabt netting.
Watford would have joined QPR and Millwall on six points had they held on for a win at home to Coventry City, who they lead 2-0 with two minutes of normal time left.
David Bell pulled one back after 88 minutes and a stoppage-time penalty from Lukas Jutkiewicz saw the Sky Blues come back for a surprise point. Will Buckley and John Eustace had looked to have the Hornets on course for a win.
With Leeds United and Nottingham Forest due to clash on Sunday, Preston North End are the only side to have lost both their outings this season. They were hammered 4-0 at Swansea City to drop to the bottom of the table.
Stephen Dobbie, Darren Pratley, Nathan Dyer and Dave Cotterill scored for the Welsh side.
Portsmouth were denied a morale-boosting win at home to Reading when Jimmy Kebe scored an 87th-minute equaliser in a 1-1 draw. Nadir Ciftci had put Pompey ahead after just eight minutes.
An 87th-minute goal from Chris Burke gave Cardiff City a 2-1 win at Derby County.
Michael Chopra had put the Bluebirds ahead at Pride Park, with Tomasz Cywka levelling before the half-time break.
The former Iron forward Billy Sharp converted a stoppage-time penalty for Doncaster Rovers to secure a 1-1 draw at home to Bristol City.
Damion Stewart thought he had the Robins on course for a win under new manager Keith Millen.
An own goal from Patrick McCarthy after 35 minutes gave Barnsley a 1-0 victory over Crystal Palace at Oakwell.
Ipswich Town and Burnley drew 1-1, with both goals coming in the final stages. The Tractor Boys took the lead after 86 through midfielder David Norris, with defender Clarke Carlisle levelling for the Clarets in stoppage time.
Leicester City and Middlesbrough played out a goalless draw at the Walkers Stadium.