Nathan Fisher scored twice for Gateshead as Mansfield Town conceded four goals for the second game running.
The Stags, who on Saturday, fell behind when Liam Hatch nodded in but drew level from Luke Jones's powerful header soon after.
Fisher's 18-yard shot put Gateshead ahead again and Chris Bush's long-range effort made it 3-1.
Mansfield's Lee Beevers was sent off for two yellow cards before Fisher added his second from inside the box.
VIEW FROM THE DRESSING ROOM
Mansfield Town manager Paul Cox told BBC Radio Nottingham:
"I'm fuming. One-one at half-time was probably a fair score but there was a lack of discipline, desire and application in the second half. There was a sloppiness defending our goal area.
"There were some harsh words said and action need to be taken, We have a decent squad and changes will have to be made.
"I will speak to the players individually and what is said will stay behind closed doors.
"But something has to be done. We are two games in and it's not good enough by a country mile. I will have to do something about it.
"I apologise to the fans. They have been brilliant and they need an apology. I promise I will work hard to turn that around because it's not good enough."