Newcastle's young reserve side were beaten by Northern League outfit Newcastle Benfield in the club's opening friendly of the campaign.
Keegan was joined by Terry McDermott, Chris Hughton and Arthur Cox on the touchline.
Ryan Donaldson put Newcastle ahead on two minutes, set up by Mark Doninger.
Benfield quickly turned things round to go 2-1 up but Jonny Godsmark levelled the game up at 2-2 before the home side rained in goals to go in 5-2 up at the break.
Reserve team coach Adam Sadler: "We're disappointed but we have to use pre-season to look at fitness not just performance.
"The lads though were disappointed to concede six but if you don't defend properly you get punished."