The Lions were buoyed this week by the news of a potential multi-million pound investment from a US finance company.
And they certainly looked upbeat in what was a comfortable home win for Willie Donachie's ever-improving side.
However, it was a good start by the visitors and Adam Connolly forced Lenny Pidgeley into a good early save with a curling shot.
Defender Shane Duff also headed wide from a corner in the first ten minutes before Byfield produced Millwall's first shot.
If anyone was going to kick-start the home side, it was going to be their impressive top-scorer.
On 14 minutes, Byfield showed why he is such a threat by bursting in-between the two sleeping Cheltenham centre-backs and forcing Shane Higgs into a fine stop.
But the next time the former Aston Villa man was gifted with such an opportunity he was to make no mistake.
Dave Brammer found Tom Brighton on the left-hand side on 33 minutes and the Scotsman swung in a perfect cross leaving Byfield with a point-blank header and his 13th goal of the season.
But as it so often happens, Millwall went to sleep slightly after opening the scoring and were lucky not to concede five minutes later.
Big Damian Spencer chested down a Sosthene Yao ball into the path of an unmarked Connolly, who wasted a great chance with a weak shot straight at Pidgeley.
And he was made to pay just four minutes later when Millwall doubled their tally. Brighton beat the Cheltenham offside trap to race on to a Neal Ardley ball and slot home his first goal for the club he joined in the summer from Clyde.
Again, the visitors made a decent start to the second half with Dave Bird flashing a shot just wide moments after coming on as a substitute.
But Millwall always had that little bit more class in attack, which they proved on 64 minutes when Byfield got down the left and put in a superb cross for Neil Harris, whose diving header it the side-netting.
Cheltenham offered little else to reduce the deficit in the remainder of the game and a recent good run has now come to an abrupt end with this their second straight defeat.