From the Super Mario Wiki
The High-Jump Save is a Power Shot that is used in Mario Tennis: Power Tour. It is used by Mel in the story mode, who versed in the Island Open. In order to obtain the save for Ace and Clay's usage, L3 Jump is required. Upon activation, the user will do a high jump and land next to the ball, hitting it. The saves reach isn't very big, but it can hit a ball that is higher than normal. It is also an upgraded version of the Lunging Save.
"A powerful Lunging Save that can reach balls higher up."