New West Ham manager Slaven Billic was introduced before the game to a sell-out crowd, who were lapping up the sunshine at this unusual time of the year for a competitive fixture.
The Hammers had academy manager Terry Westley in temporary charge for the visit of the Andorrans and Sakho grabbed two first-half goals before James Tomkins headed home a third on 59 minutes.
Westley decided to play a youthful side that included Reece Oxford, who became West Ham’s youngest-ever first-team player at just 16 years and 198 days old.
The central midfielder was thrust straight into the action and found himself in the referee’s book after 15 minutes as he was a little bit too eager to impress and left his studs in on Pablo Aguilar.
One of the more experience heads in the side was Sakho and he should have given his side the lead on 30 minutes but he could only head over the crossbar from six yards after some good work down the right by Joey O’Brien.
The home fans would have been starting to sweat a little more profusely as the half wore on as their side struggled to break down the dogged visitors – but the opening goal did eventually come on 37 minutes.
Sakho was the man on the scoresheet, meeting a Mauro Zarate cross from the right with a powerful header.
That goal was just the start for the hosts, who doubled their lead right on half-time.
Sakho again finished off a delivery from the right after some quick build up by play from O’Brien and Zarate.
Things slowed to pre-season pace in the second-period but West Ham were always in the ascendancy and Tomkins headed home 14 minutes into the half after some nice work by Matt Jarvis.
Westley rang the changes in the last 25 minutes with Josh Cullen putting in an impressive cameo that deserved a goal.
He went close with five minutes remaining but his cultured shot from the edge of the box cannoned back off the crossbar.
The teams meet again in Andorra for the second leg on Thursday 9 July.