The Scots produced a second-half fightback to overturn a 21-3 deficit at the break and record a morale-boosting 25-21 victory despite having the Glasgow prop red carded afor high challenge on French hooker Pierre Bourgarit in the 50th minute.
Fagerson was initially yellow carded before having his punishment upgraded to a red after a review via the newly-implemented bunker system.
With just two warm-up matches remaining - away to France and at home to Georgia - the Scots fear any suspension for Fagerson could carry over into the World Cup.