Sakho went from Europa League hero to villain by being sent off after just 14 minutes against FC Lusitans on Thursday night.
Sakho's first-leg double helped the Hammers on their way to a 3-0 win which all but guaranteed their progress going into the return against the Andorran minnows.
But Sakho saw red after an off the ball incident in Bilic's West Ham dugout debut and will now miss at least the second qualifying round first leg against Maltese outfit Birkirkara next week.
Rookie striker Elliott Lee's winner ensured the ten-man Hammers cruised through but Sakho's sending off was the major talking point.
Lusitans usually average 100 fans for home games but 550 showed up for the biggest game in their 16-year history, meaning they weren't outnumbered by the travelling, hardcore Hammers.
Those who couldn't get into the sold out 1100 capacity Estadi Comunal, which had just two tiny stands, watched on from a campsite in the hills overlooking the ground.
With allotments and the Pyrenees mountains making up the rest of the picturesque backdrop and the game played 1000m above sea level in the highest capital city in Europe West Ham are unlikely to have played in such an unusual and eye-catching setting.
The niggly edge, and Lusitans' play-acting, from the first-leg continued in the second.
And Sakho paid the price when he got sucked into a scuffle with Moises San Nicolas and was sent off for his part in the altercation.
West Ham responded when Lee slotted in his first Hammers goal on his full debut to kill off any ideas Lusitans may have been getting of causing an upset.
As it turned out West Ham had nothing to worry about. Lusitans didn't register their first shot on target in the whole tie until the 74th minute of the second leg.
Birkirkara, whose star player is 36 year-old former Italy striker Fabrizio Miccoli, will hope to provide a bit more of a test.
WEST HAM: Randolph 6; O'Brien 6 (Burke 61, 6), Tomkins 6, Oxford 7, Page 7; Almafitano 4 (Parfitt-Williams 76), Poyet 7, Cullen 7 (Nasha 86), Jarvis 7; Lee 7, Sakho 3.