At 5-4 in the second set, Martinez even made an on-court coaching appearance.
"I figured out that it might be good for me to hear some things," Muguruza said before closing it out.
Muguruza's main coach Sam Smyuk will join her team in Dubai. Martinez, a fellow Spaniard and former world No. 2, won Wimbledon in 1994 as well as reached two Grand Slam finals.
"Conchita and I [have] known each other since I was little, and she's always been a little bit in the shadow, helping me here and there," Muguruza said. "I thought that it might be a good idea to have her in the next couple of tournaments into Miami."
The 45-year-old Martinez enjoyed an 18-year career complete with 33 WTA titles, five Fed Cup championships and three Olympic doubles medals.
"I think she's a very calm person, and she has a lot of experience," Muguruza said. "This is not easy to find and it isn't easy also to get in this difficult competitive environment [and] get along with somebody very good."
