As Sloane Stephens said she had to run down a lot of balls "...left me completely exhausted/fatigued both physically and mentally."
That's typical for two-hand players who rely only upon long rallies.
Many "unseasoned" players want time to savor their lastest win, it's understandable; they don't know when the next win will be.
That's the disadvantage of two-hand strokes, you must run more, you have a shorter reach, and prefer defensive tennis as opposed to " shooting the rapids," agressive net play, daring, in-your-face Tennis.
Two hands is batting the ball, that's what baseball players do. Two handed play is like riding a bike, and not taking the training wheels off.
Daniel A. Young, Sr.
Nttcacemaker.com
"Teaching Tennis the way it ought to be taught."