Sam Winnall has put Barnsley level moments before half time in their League One clash with Millwall at the New Den.
After a cagey start from both sides, Marley Watkins almost gave the Tykes the lead on 11 minutes as the forward forced a low save out of David Forde.
Lewin Nyatanga then missed the target with a header for Barnsley before Dan Crowley blazed over as Millwall, who lost 4-0 at home to Coventry on Saturday, struggled to gain a foothold in the game.
Winnall went close again for the visitors, but Neil Harris's side managed to take the lead on 26 minutes after Fred Onyedimna latched onto Ed Upson's cross before scoring from close range.
Just before the half-hour mark, Millwall could have edged further head when Shaun Williams fired wide of Adam Davies's goal with a shot from a tight angle.
With the break approaching, Steve Morison also went close for the Lions, but Winnall put the Tykes back on terms by heading home from Watkins's cross.
