Spillover　of　adsorbed　species　from　one　active　site　to　another　is　a　key　step　in　heterogeneous　catalysis.　However,　the　factors　controlling　this　step,　particularly　the　spillover　of　polyatomic　species,　have　rarely　been　studied.　Herein,　we　investigate　the　spillover　dynamics　of　H*　and　CH3*　species　on　a　single-atom　alloy　surface　(Rh/Cu(111))　upon　the　dissociative　chemisorption　of　methane　(CH4),　using　molecular　dynamics　that　considers　both　surface　phonons　and　electron-hole　pairs.　These　dynamical　calculations　are　made　possible　by　a　high-dimensional　potential　energy　surface　machine　learned　from　density　functional　theory　data.　Our　results　provide　compelling　evidence　that　the　H*　and　CH3*　can　spill　over　on　the　metal　surface　at　experimental　temperatures　and　reveal　novel　dynamical　features　involving　an　internal　motion　during　diffusion　for　CH3*.　Increasing　surface　temperature　has　a　minor　effect　on　promoting　spillover,　as　geminate　recombinative　desorption　becomes　more　prevalent.　However,　the　poisoning　of　the　active　site　can　be　mitigated　by　the　frequent　gaseous　molecular　collisions　that　occur　under　ambient　pressure　in　real-world　catalysis,　which　transfer　energy　to　the　trapped　adsorbates.　Interestingly,　the　bulky　CH3*　exhibits　a　significant　spillover　advantage　over　the　light　H*　due　to　its　larger　size,　which　facilitates　energy　acquisition.　These　insights　help　to　advance　our　understanding　of　spillover　in　heterogeneous　catalysis.　Under　real-world　conditions,　the　frequent　collisions　of　gaseous　CH4　molecules　on　Rh/Cu(111)　single-atom　alloy　are　a　key　to　promote　adsorbate　spillover,　especially　for　bulky　polyatomic　CH3*　species,　providing　insights　into　the　effective　use　of　spillover　in　heterogeneous　catalysis.　image