'Jeopardy! Masters' Host Ken Jennings Declines Rematch with James Holzhauer

The "Jeopardy! Masters" tournament has host Ken Jennings' arch nemesis back in the game, but don't expect Ken to give in to the trash talk being thrown his way -- he tells us he's hung up his buzzer for good.

Ken joined us Tuesday on "TMZ Live" to respond to James Holzhauer, who's playing again in the 'Masters' tourney ... and who called out Ken during Monday night's episode. 'Jeopardy!' fans know Ken and James were long considered #1 and #2 in the all-time rankings -- they went head-to-head in 2020's 'G.O.A.T.' (Greatest of All Time) tournament, and Ken came out on top.

Last night, James playfully demanded Ken give him a rematch -- but KJ tells us it ain't gonna happen. He says he's happy just to have defeated James once ... plus he's digging being the host now, instead of playing.

For now, Holzhauer will have to settle for taking on 5 other champs for a $500K prize and a Trebek Trophy.

Ken says he's thrilled to be watching the action from his hosting podium, adding ... the competition is already really fierce.