Saha also said the team's immediate goal is to win first Test against Sri Lanka and carry the momentum for rest of the series.
Saha revealed how hard is to keep wickets when Ashwin gets to bowl as the off-spinner possesses a lot of variations under his sleeve.
Sri Lanka lost all nine matches - three Tests, five one-day internationals and a Twenty20 global - as they were humiliated at home by Virat Kohli's tourists from late July to September.
"We have played many matches in Ranji, India A and during practice".
"We are yet to see the wicket". This will be a challenging series for us.
In a bumper home season, which started in September 2016, India won 10 of 13 test matches, with their solitary defeat coming against Steve Smith's Australia.
India, the number one Test side in the world, will go into the home series as favourites.
"The series against India was a huge learner for us".
Coach Nic Pothas, who took over after Graham Ford left in June, said the India debacle had taught his team vital lessons.
"It's internal - the discipline, the culture and how the teams stick together", Pothas said. The more you keep, the better idea you develop.
"We know they are a good side. But we played them months ago", the South African added.
All-rounder Mathews, who is returning from a calf injury that made him miss the Pakistan Tests, will be employed exclusively as a batsman.
Kohli's India are looking to consolidate their top Test ranking and keep their winning run intact on home soil.
Talking about the upcoming tour of South Africa, Saha expressed, "Every match is important for us".
Kohli and his boys will now have extra motivation to go for a clean sweep in the three-match Test series.Wicket-keeper Wriddhiman Saha on Monday said that his team's first target is to win the opening Test at the Eden Gardens to set the momentum for the three-match series against Sri Lanka.
While Sri Lanka's bowling attack must find a way to stop the likes of Kohli and Cheteshwar Pujara from scoring heavily, their batsmen will have to contend with India's dual spin threat of Ravichandran Ashwin and Ravindra Jadeja.
The second Test begins on November 24 in Nagpur with the final match starting in Delhi on December 2.
Sri Lanka squad: Dinesh Chandimal (captain), Dimuth Karunaratne, Sadeera Samarawickrama, Lahiru Thirimanne (vice- captain), Niroshan Dickwella (wicketkeeper), Dilruwan Perera, Rangana Herath, Suranga Lakmal, Lahiru Gamage, Dhananjaya de Silva, Angelo Mathews, Lakshan Sandakan, Vishwa Fernando, Dasun Shanaka and Roshen Silva.