The Shrimps, who have never been beaten by Southend in seven attempts back to 2010, were drawing 1-1 with their hosts at the break.
But Bentley still tore into his players and was delighted by their response as they ran out victorious, despite the dismissal of Robbie Threlfall.
"I wasn't happy with our first-half performance and we had some very harsh words at half-time which is the first time we have had to do it this season.
"But they responded superbly with two quickfire goals.
"It was great to see and I'm delighted for Jack Sampson for scoring his first career goal because he has been unlucky this year in front of goal."