Mauro Boselli, who has returned to the club from a loan spell at Estudiantes, opened the scoring before Maynor Figueroa's 30-yard rocket and Jordi Gomez's strike gave the Latics a comfortable half-time lead.
Forest hit back after the break when Simon Cox unleashed a thunderbolt but, even with Wigan defender Antolin Alcaraz's red card in the 78th minute, the visitors managed to keep Forest at bay, with Callum McManaman's last-minute goal sealing the win.
"I was very pleased with the whole game," Martinez said.
"I thought the first half when you get the clinical finish it is very pleasing but it was a game full of good football, great goals from both teams.
"For a team that has made seven changes and hasn't played very much together, to be able to cope with going down to 10 men I was very pleased.
"Young players coming in who have been working really hard and are desperate to share the demands that we're going to have this season so I'm very pleased.
"Last year, two seasons ago, three seasons ago, we always tried to show that depth in the squad and we always tried to be competitive so it's very pleasing that we used players that haven't been involved and they showed the level we have today."