Aleksey Shved's late basket ensured Khimki opened the Top 16 with a dramatic 91-89 win over Russian rivals CSKA Moscow at the Krylatskoye Arena.
CSKA led 51-41 at the interval, but Shved took charge of the game with 16 points in the third quarter, bringing Khimki to within two.
The 27-year-old then sunk a field goal with 1.1 seconds left on the clock, taking his points total for the night to 28 - 22 of which came in the second half - to put the hosts in charge at the death, with Moscow point guard Milos Teodosic missing a fade-away effort to level the match at the buzzer.
Olympiacos overcame Barcelona 74-62 in their Group F opener at the Peace and Friendship Stadium.
The Greeks eliminated the Catalan side in last season's quarter-finals in dramatic fashion and they were victorious once more, Vassilis Spanoulis starring with 11 points and nine assists.
Olympiacos surged into a 39-26 lead at the interval, and, although Ante Tomic scored 16 points, Barcelona were unable to mount a comeback with nine opposition players providing at least six points to the cause.
Unicaja Malaga got their Top 16 campaign off to a winning start by beating Darussafaka 70-62.
The Turkish side - featuring at this stage for the first time in their history - led by three points at half-time but fell to a second away defeat against the Spanish team this season.
Edwin Jackson led a late charge for Malaga, scoring 13 of his 20 points in the fourth quarter to help overturn the deficit and ensure a winning start.