The Hammers staged somewhat of an upset, as they got the better of City 2-1 at the Etihad Stadium in the Premier League.
Chelsea-owned winger Victor Moses put West Ham ahead after just six minutes, and Diafra Sakho doubled the advantage just past the half-hour mark.
Kevin De Bruyne fired home for City on the stroke of half time, but West Ham kept out City in the second 45 minutes.
Poyet, who joined Championship outfit MK Dons on a season-long loan deal from West Ham in the summer transfer window, was delighted to see Slaven Bilic’s side pick up all three points at the Etihad.
What a result for the boys! Buzzing for them! 2nd in the table COYI— Diego Poyet (@diegopoyet7) September 19, 2015
Absolutely Brilliant today @whufc_official - so proud— Lady Karren Brady (@karren_brady) September 19, 2015
The win at the Etihad has lifted West Ham up to second in the Premier League table with 12 points from six matches, just three points behind leaders City.