The Latics have been on Espinoza's trail since his outstanding performances for Honduras during the Olympic tournament last summer.
And now Roberto Martinez has finally got his man, the 26-year-old midfielder is eager to get going.
"It's taken a while to get all the paperwork done but now I can concentrate on fighting for my place," said Espinoza.
"I just want to say a big thank you to everyone at the club who have been working so hard to get everything through in time - and for the manager to have the belief in me.
"Now it's down to business."
Espinoza's last appearance on English soil looks to be a microcosm of what Wigan fans can expect from the player, who moved to the USA when he was 12.
In the Olympic quarter-final against Brazil at St James' Park, Espinoza earned a standing ovation for his tigerish display and scored a brilliant goal only to get himself sent off near the end of an agonising 3-2 defeat.
Espinoza collected yellow cards in his other two Olympic appearances, adding to the five he got in the MLS last term, in addition to one red card, so evidently the midfielder is not afraid to tackle and - suspensions permitting - should bring some steel to the Latics midfield.
"He is an excellent talent and every time we have seen him play he has shown the desire that we like to see from our players," said Martinez.
"The Olympics in the summer gave a great example of just what he can do on the pitch, especially in his performances against Spain and Brazil."
The problem for Martinez though is that Espinoza will have just 24 hours with his new team-mates before being plunged into the English game.
"Usually players would have more time preparing for their debut and getting used to their new team-mates, but Roger is so desperate to play as soon as he can," he said.
Espinoza will not be Wigan's only debutant on Saturday as Manchester United striker Angelo Henriquez will make the first appearance of his loan spell.
With Spain Under-21 keeper Joel also trying to impress during his trial period, it has already been a busy transfer window for the Latics.
And, whilst it may take some time, Martinez anticipates a further arrival this month as he tries to steer his team away from the drop zone.
"We want to bring in one more outfield player during this window, and that is what most of our work is focused on," he told the Wigan Evening Post.
"Then I would feel we were fully equipped to handle the second part of the season.
"It's not something that is going to happen overnight - I think it might go all the way to the end of the window.
"But we are prepared to wait as long as it takes."