Moses stunned the home crowd by scoring the first goal against the Blues in the Premier League this season, collecting the ball from Dimitri Payet 30 yards out, advancing and unleashing a wicked low shot into Joe Hart's bottom corner on five minutes.
It was soon 2-0 when City failed to clear a corner and it fell to Sakho, who slotted home a neat finish under pressure inside the six-yard box.
But the real stars of the show were Winston Reid and goalkeeper Adrian, who were impenetrable in a second half dominated by the Blues to secure an unlikely hat-trick of away wins for Slaven Bilic's side who find themselves in second place after six games.
Adrian – 9
There were some question marks over whether Bilic would bring the number one back in after he missed the last three games through suspension. Darren Randolph has done well in his absence, but Adrian fully justified his inclusion pulling off a string of fine saves in the second half whenever City did break through the Hammers' resolute defence.
Jenkinson – 7
Getting back to something like his best form with a very dogged display against the likes of Raheem Sterling and Alexandar Kolarov. Got forward on more than one occasion and very nearly set up a goal for Sakho. Grew tired late on suffering bouts of cramp and was withdrawn for James Collins.
Tomkins – 8
James Tomkins has started four Premier League games for West Ham this season and Bilic's side have won all of them. That is no coincidence and his reading of the game and composure was vital throughout. Defended intelligently and when he was beaten his rock solid partner Reid was there to mop up.
Reid – 10
Reid put in yet another faultless display to underline his reputation as one of the best defenders in the Premier League. He was everywhere and was a constant thorn in Manchester City's side. He really is the rock on which West Ham can build a very exciting future. Man of the match hands down.
Cresswell – 7
Cresswell got up and down and was a real threat in the first half despite the danger posed by Manuel Pellegrini's side if he did venture too far forwards. In the second half, though, he was pegged back by Jesus Navas' pace. He coped admirably and stopped a number of crosses coming into the box but needed help from his teammates on a number of occasions when Navas did breeze past him. The positive for Cresswell is that he probably won't face a more difficult opponent all season.
Lanzini – 8
West Ham's 'man of the match' in the 3-0 win over Liverpool at Anfield, the little Argentine put in another great performance against City. He was composed, showed great skill and put in a brilliant shift for his teammates. Also played intelligently after being booked a third of the way through the game and didn't dive in or make rash challenges. Was subbed late on for Nikica Jelavic.
Noble – 7.5
Had a brilliant first half helping out his defence and linking the play to set up counter-attacks. Chasing shadows a bit second half in the City onslaught but kept at it and did not lose focus. Has most definitely been reinvigorated by increased competition for places and being given the captain's armband following Kevin Nolan's departure.
Obiang – 7.5
West Ham missed Kouyate through injury but Obiang ensured the impact was mitigated by putting in an energetic display based on his excellent passing game. Sat in when needed and broke forward with purpose, epitomised a key word for the Hammers midfield "composure" not panicking in tight situations and playing positive forward passes at the right times, looks a real find.
Moses – 7
Scored a fantastic low rocket on five minutes to give West Ham the lead and ultimately helped his parent club Chelsea back in the title race at the same time. Showed pace, power and strength and was a threat going forwards as well as helping out at the other end. A lack of matches this season told in the second half in terms of fitness and he was replaced by Michail Antonio for his Premier League debut.
Payet – 7.5
After a playing a starring role in most games this season all the pre-match hype was about the Hammers' French hero. And while he did not get on the ball as much as he usually does given the quality of the opposition, when he did he hurt the hosts. So good on the ball and set up the first for Moses before delivering the corner which led to West Ham's second. On this form Payet really is the club's best player since Carlos Tevez.
Sakho – 9
Got his goal, a real poacher's finish inside the six-yard box. But that was just the icing on the cake really from Sakho who literally ran himself into the ground for his team once again. Chased lost causes, ran the channels, closed the centre-backs, closed Hart, closed the full-backs, tracked back to help defend, held the ball up well and was a constant threat in behind. A brilliant example of how to play the lone striker role to full effect.
Antonio – 6
Hardly touched the ball but when he did needed to look after it a little better as West Ham were under intense pressure. Was brought on for Moses with a view to taking the ball on 40 or 50 yard runs to give his team some breathing space. But the way the game had panned out by that point meant it was a case of digging in. Showed he has pace to burn on a couple of occasions.
Jelavic – 6
Did not see too much of the ball but made a nuisance of himself and closed City's defenders down. Didn't show anything that would suggest he will seriously challenge the likes of Sakho and Carroll for a first team spot. It is a shame that he cannot play at Leicester City in the League Cup on Tuesday night as he is cup tied because he could do with the minutes under his belt.
Collins – 7
Hammers fans' favourite entered the fray late on for Jenkinson and showed no signs of rustiness winning a few trademark headers as City threw the kitchen sink at the visitors. Even if it is from the bench, Collins is a vital squad member for West Ham.