Despite the setback, the Forest boss described the Reds' performance as their best of the campaign so far, having won each of their previous three outings.
Kieran Dowell in action for Nottingham Forest
And Dowell's performance was particularly impressive, as far as may of those present at Oakwell are concerned, with some already believing him to be better than Zach Clough - the man he replaced in Warburton's eleven.
Here's what they've been saying on Twitter:
Dowell pulls strings in that hole— Whysall14 (@Josh_nffc) 15 August 2017
Can we just send Clough to Everton and keep Dowell? He's something else alright! #NFFC— NorthWestRed (@red_till_death) 15 August 2017
Dowell is absolutely unbelievable. Far too good for this league #nffc— Lewis Staniforth (@LStaniforth92) 15 August 2017
I love Zach, but Dowell is light years better than him. An absolute baller #nffc— Gareth (@DavidGBarker) 15 August 2017
With Ross Barkley out of contract next summer, Everton will no doubt be keeping a keen eye on Dowell's progress at Forest, with the 19-year-old a potential heir to the England international.
And Dowell is sure to be encouraged by the progress of Mason Holgate, Ademola Lookman and Dominic Calvert-Lewin, who've all enjoyed runs in Everton's first team following spells in the Football League.
Matty Pearson and Ryan Hedges scored either side of Daryl Murphy's equaliser for Forest to secure Barnsley's first points of the campaign.
Will Dowell's Nottingham Forest spell get him ready for Everton's first team?