Walker made a sensational return to Europe's biggest stage, powering Besiktas to a thrilling 103-101 road victory over Virtus Bologna.
In a dramatic encounter decided by a remarkable late turnaround, the American guard posted a Performance Index Rating (PIR) of 36, easily outshining every other player across the round.
He poured in 30 points (shooting 2/4 from two-point range, 7/11 from beyond the arc, and 5/9 from the free-throw line), while also tallying four rebounds, five assists, and a steal.
Dusan Alimpijevic's side trailed by 13 points (97-84) with just over three minutes remaining before staging a stunning comeback, sealed by Conor Morgan's buzzer-beating three-pointer.
Besiktas now turn their attention to next week's EuroLeague Round 10 home fixture against Zalgiris, where the Istanbul side will look to secure their fifth victory of the campaign.
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VIDEO: Alimpijevic's Besiktas Stuns Virtus: Last-Second Three-Pointer Caps Massive Comeback to Silence Bologna!