With Muguruza's full-time coach Sam Sumyk back home awaiting the birth of his child, Fed Cup captain Martinez stepped in.
No Spanish woman had won the Wimbledon singles title since Martinez 23 years ago but Muguruza was superb all fortnight and defeated Venus Williams 7-5 6-0 in the final.
Williams, 37, was the oldest woman to make the final since Martina Navratilova, who just happened to lose to Martinez.
And when Martinez discovered Muguruza had beaten Williams in Rome this year, just as she had beaten the 37-year-old Navratilova in the Italian capital, the coincidences became too much.
Martinez kept her own experiences out of the pre-match preparations, saying: "We talked about it many times, not before the match, it was a whole different match. It wasn't about me, it was about what she had to do to beat Venus and not focusing on age or anything.
"But, inside of my mind, there were too many coincidences - (the opponent was) 37, she beat her on clay this year in Rome, I beat Martina on clay in Rome, so I was like, 'Okay, we're going to do this'. I believe in those things."
Muguruza made her first big breakthrough by reaching the final of Wimbledon two years ago, losing to Serena Williams, and then turned the tables on the American to win her first grand slam title at the French Open last summer.
But as the expectation piled up, the wheels came off, and less than a week before the start of Wimbledon Muguruza lost 6-1 6-0 to Barbora Strycova in Eastbourne.
Martinez deserves a huge amount of credit for the work she has done with Muguruza during this fortnight.
She said: "We talked a lot. I tried to build her confidence. She was very open and very positive throughout the whole tournament. I just tried to coach her the best I know.
"It feels really great. To be working with her for this time and to see her do so well in every single match she's played, I'm really proud of her and I'm really happy to be part of her win."
Martinez knew right from the start her player could be the one holding the trophy, but it was a fourth-round victory over top seed Angelique Kerber in probably the match of the tournament that convinced her.
"She's got an amazing game, amazing potential and she was doing great," said Martinez. "Every day that was going by I thought she was playing amazing.
"After she beat Kerber, that match was so tight, but she hung really tight. Of course I thought she could do it but you have to be so focused for a couple of weeks here, it's not easy and she did it.
"The whole two weeks I think she's played every point of every match. That mentally is very strong and you can see players break down with that."
Martinez does not expect Muguruza to suffer the same let-down as she did after winning the French and hopes she can be more consistent.
"She's going to have more experience," said the 45-year-old. "She had ups and downs but she already has a couple in her pocket and another final.
"Hopefully she can stay a little bit more steady. The key is to continue to work hard and to focus in every tournament.
"It's worth doing it, the other tournaments are very important for your career too. Hopefully that's going to sink in."
It has clearly been a hugely successful partnership but Martinez is happy to take a back seat again.
"I'm always hanging around," she said. "I'm still the Fed Cup and Davis Cup captain and I'm always in contact with every player. But Sam is going to step in now."
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