Leading 3-1 from the first leg on Thursday, Liberia trailed to former Middlesbrough striker Kei Kamara’s 55th-minute goal before conceding an injury time penalty – one which, if successfully converted, would have ended their chances of making it to Qatar.
However, teenage ‘keeper Ashley Williams dived low to his left to keep out Umaru Bangura’s spot kick, with the game brought to a close just seconds later.
Sangare came on just before the hour mark to earn his fourth international cap.
Closer to home, defender Fabian Schär was involved from the outset as Switzerland coasted to a 4-0 win over Gibraltar in Sion, boosting their hopes of automatic qualification for Euro 2020.
The Swiss are currently third in Group D but have a game in hand on both the Republic of Ireland and Denmark. They travel to Copenhagen next month before hosting the Republic in Geneva.
In Group F, Emil Krafth remained on the bench as Sweden picked up a useful point against Norway in Solna. The visitors would have leapfrogged their Scandinavian neighbours into second place, behind Spain, with victory, but another Emil – RB Leipzig’s Forsberg – struck after the break to cancel out Stefan Johansen’s first-half opener.