The match has been billed as the battle for fourth place in Pool C behind Wales, Fiji and Australia but Maisashvili said there was plenty still to play for despite Georgia's opening loss to the Wallabies.
"In a way, it is a bit of a final, but it's also just the beginning," he told reporters in Toulouse on Thursday.
"We've only played one match, even if we lost it. Yes, it's an important match against Portugal but we're concentrating on our team."
Maisashvili was able to recall Lyon loose forward Beka Saghinadze into a starting team featuring eight changes from the side that lost 35-15 to Australia at the Stade de France.
Saghinadze, who missed Georgia's warm-ups and the Australia game through injury, slots into the back row at open-side flanker in place of young gun Luka Ivanishvili, who scored the first of Georgia's two tries against the Wallabies.
Fly-half Tedo Abzhandadze and scrumhalf Gela Aprasidze will start in a new half-back partnership with regular playmaker Luka Matkava dropping to the bench.
"We were disappointed after Australia. We weren't able to manage the game well and made tactical errors on a number of occasions, particularly with our kicking game," Maisashvili added.
"There was a clear lack of discipline caused by our poor game management. In the second half, we were able to get back into the game but couldn't get the result we wanted."
Centre Merab Sharikadze will captain the team for the 50th time on Saturday against very familiar opposition, the two teams having met in the final of the second-tier Rugby Europe Championship in March.
The Lelos won that match 38-11 to claim a fifth straight title and Sharikadze said they had made improvements to their game since then.
"It's true that our team have played a lot against Portugal, who have a similar style, but our style of play is much more balanced now," Sharikadze added.
Georgia Team:
15-Davit Niniashvili, 14-Akaki Tabutsadze, 13-Giorgi Kveseladze, 12-Merab Sharikadze (captain), 11-Alexander Todua, 10-Tedo Abzhandadze, 9-Gela Aprasidze, 8-Beka Gorgadze, 7-Beka Saginadze, 6-Tornike Jalaghonia, 5-Kote Mikautadze, 4-Lado Chachanidze, 3-Beka Gigashvili, 2-Shalva Mamukashvili, 1-Mikheil Nariashvili
Replacements: 16-Tengizi Zamtaradze, 17-Guram Gogichashvili, 18-Guram Papidze, 19-Nodar Cheishvili, 20-Giorgi Tsutskiridze, 21-Vasil Lobzhanidze, 22-Luka Matkava, 23-Demur Tapladze