McManaman was one of seven changes the Spaniard made for the 4-1 win, but was not informed he was starting the match by his manager until the last minute as he is prone to extreme nerves ahead of kick-off.
As a result, the 21-year-old only discovered he was in the starting XI this morning, and responded with a goal and a solid all-round display as the Latics marched into the quarter-finals.
"He's a real talent," Martinez said of McManaman.
"He's an old-school footballer but he gets really hyped-up for the games, and we told him yesterday that he wasn't playing so that he would not be upset overnight and just concentrate on having a good sleep.
"This morning when he found out he was delighted - and it showed in his performance because he managed 90 minutes for the first time this season."
McManaman, a distant relative of former Liverpool winger Steve McManaman, and midfielder James McArthur were two of the players recalled by Martinez and both shone.
McManaman struck a fine opening goal in the 31st minute and Arouna Kone tapped home a second shortly before the break to leave new Huddersfield manager Mark Robins with a difficult half-time team-talk in his first match in charge.
McArthur struck a brilliant third early in the second half and although Huddersfield substitute Lee Novak headed home just after the hour, Kone added a late fourth.
Wigan are through to the last eight for the first time in 26 years, where a trip to the winners of the replay between Everton and Oldham awaits.
"It's a great tie," Martinez told ITV.
"Oldham have been magnificent and it is still an open game, so we will follow that one with interest. It's a great game for the sixth round."
Reflecting on his side's cup run, he added: "Every game is a priority. What's important as a football club is that you are capable of facing two competitions. I think two, three, four years ago, we never had the opportunity to have a pool of 16-17 players and now we have that strength.
"That's why I'm so proud today. After the changes that we made, we looked like a team, we had real understanding of what we were doing. And that is a real credit to the people behind the scenes."