Miller stopped the 35 shots he faced -- six by high-scoring Alexander Ovechkin and five by Nicklas Backstrom.
Gerbe added one assist and Derek Roy two for the Sabres, who avoided a third straight loss.
Net-minder Jose Theodore was beaten three times on 28 shots for the Capitals, who had not lost since a 4-3 overtime setback on Nov. 23 at Ottawa.
They beat the Sabres 2-0 in Washington on Nov. 25 and had gone 4-3 in previous contest against Buffalo.
2014: The Year in Fashion [PHOTOS]
LeBron James reveals his new Nike shoes