San Antonio can clinch the series in Game 6, which is set for 9:30 pm ET on Thursday on TNT.
If the Spurs do eliminate Memphis they will play Houston in the Western Conference semi-finals.
Spurs reporter Kelsey Bradshaw also says that the handwriting in the above tweet matches that of the San Antonio head coach.
The Grizzlies had managed to contain Mills in the first four games, but he broke the shackles with a 20-point haul in game five to enhance his reputation as a big-game player. The Spurs look to sway the recent surge by Memphis in the friendly confines of the AT&T Center in San Antonio, as both teams have taken games on their home floor, respectively.
The Grizzlies outlasted the Spurs and overcame Kawhi Leonard's career-high 43 in Game 4 Saturday on a Marc Gasol floater with 0.7 seconds left in overtime. Led by Mike Conley (who finished with 26 points), the Grizzlies clawed their way back into the game, cutting the deficit to four points early in the fourth quarter.
Mills shot a scorching 7of-10 from the field, including 5-of-7 from the three-point line.
The Thunder's Russell Westbrook had another superhuman game with 47 points, 11 rebounds and nine assists but did not receive enough help from his supporting cast.