Craig Dawson scored late in the first half before Issa Diop and Jarrod Bowen helped the Hammers to go six points clear.
"The main thing is topping the group. The home games are vitally important. We want to win away too," Bowen told BT Sport.
"If we can stay strong, keep the confidence then I think teams will be fearing us. We could be the team to look out for. We're only a few games away from a big cup run," he added.
Elsewhere in the group Rapid Vienna beat Dinamo Zagreb 2-1 to open their account in the competition.
Lyon have also made a perfect start to the European campaign and came from behind to edge Sparta Prague 4-2.
