Galle - The traditional moving day on Friday will be decisive for the Proteas, as they look to set up a winning position in the first Test match against Sri Lanka in Galle.As it happened: SL v SA - Day 2JP Duminy's hundred led a spirited lower-order fight back to give the Proteas a commanding first innings total, but the onus has shifted to the bowlers, who will need to make inroads to take firm control of the match. "It's going to be a lot of hard work," Duminy said after the day's play on Thursday. "The wicket is pretty flat for the seamers, but there is a little bit there for the spinners. "The game will probably speed up on day four and five so tomorrow is going to be a crucial day to set up those last two days." Duminy's key partnerships of 75 with Vernon Philander (27) and 66 with Morné Morkel (22) hurt Sri Lanka's weakened attack , but more importantly, highlighted his value in that position. "The biggest challenge was the spinners," he said."Trying to marshal the partnership as best as possible, especially with Morné. "Vernon and I have played together a long time so we sort of understand each other's games."Marshalling that partnership with Morne was crucial, and to see how he applied himself today was exceptional." Duminy was tasked with the responsibility of leading the lower-order, who put in a worthy performance to add 187 runs to the overnight score. He says he is enjoying his role at number seven, and understands how it fits in with the current make-up of the side. "It's always pleasing to get to three figures in these conditions," he said."I think understanding my role within the team is more crucial."Batting at seven and trying to marshal the lower order as best a possible has always been key for me. "The hundred will come if I bat as long as possible, so I'm pretty pleased with getting the ton here today. "There is still a lot of hard to be done, there might still be an opportunity for a job with the ball so there are still three big days to come."