Ba felt the full force of the Argentina international's boot in his face as the pair challenged for a 32nd-minute loose ball, which the striker headed inches wide with the score at 0-0.
Benitez, whose side has now not won in four games in all competitions, said: "It was a penalty and a red card for me, the incident.
"In the middle of the park, you just carry on and go back from a free-kick. In the penalty area, you go back, penalty and red card.
"It changed the game. We lost one player with a broken nose, we had one substitution and we had a great reaction in the second half, but it was not enough."