Spain coach Luis Enrique made several changes to his side, with David de Gea returning in goal, while Ansu Fati was on the left of the Spanish attack and Oyarzabal returned to action after missing out on the midweek friendly in Portugal after a non-conclusive coronavirus test.
He spent another 12 months at the club in 2014-15 - also on loan - before joining Guangzhou Evergrande of the Chinese Super League.
The first half produced only one solid chance when Slovakia's Ondrej Duda tested visiting goalkeeper Darren Randolph in the final minute.
"I had already won a medal in Rio, so I am not going to be under pressure in Tokyo."
Ghana captain Andrew Ayew and Samuel Owusu were on target in the 63rd and the 65th minute to restore Black Stars' lead.
The Czech is yet to drop a set and will face fourth-seeded Sofia Kenin of the United States for a place in the final. The reigning Australian Open champion survived a fight-back from Danielle Collins in the second set and dominated the deciding one to reach the semis 6-4, 4-6, 6-0.
Spain also have two players with lightning speed - Barcelona's Ansu Fati and Wolves' Adama Traore, who impressed on his Spain debut against Portugal on Wednesday night.
Outscoring its opponent 28-14 after the first quarter, Jiangsu was never really challenged by Shaanxi over the ensuing three quarters.
"It was a tough match. We didn't play at our level in the first quarter, but changed our tactics in zone defense from the second quarter," said Shanxi coach Li Ge.
"I was expecting another level of play, something else, but it's normal. We haven't played for a year," the six-time Ballon d'Or winner said. "It's the anxiety of the first game. The important thing is to keep growing as we have done since the  Copa America.
Facing world No.6 Tsitsipas, it seemed like another one-sided match for Djokovic as the 17-time Grand Slam winner swept the first two sets and was serving for the match in the 10th game in the third set.