Roelofse, ranked 515th by the ATP, won the first set against Janowicz, the world No 24, but the Polish player hit back for a 4-6, 6-3, 6-1, 6-1 victory as the hosts secured a 3-1 win with one match to spare.
"Jerzy is ranked much higher in the rankings," Roelofse said.
VIDEO: Poland v South Africa, Day 3 highlights
"I rarely have an opportunity to play guys with this ranking, so that gave me a lot of experience.
"I started the match very well and I served great. I did everything like we planned, but then after the first set I lost some of the confidence."
The 23-year-old South African replaced veteran Rik de Voest, who withdrew from the reverse singles rubber with a lower back injury.
"Rik reported he had a really stiff lower back and couldn't play," said SA captain John-Laffnie de Jager.
"He is getting older. At first, before the tie, I thought he was going to play singles only. Then Raven (Klaasen) got injured, and given the score (1-1 after the first day), I knew that the doubles would be deciding and very important for us."
The South Africans had lost the doubles rubber on Saturday, with De Voest and Jean Andersen going down in straight sets against the Polish pairing of Mariusz Fyrstenberg and Marcin Matkowski.
On Friday, De Voest secured his team's only victory of the tie with an impressive win against Lukasz Kubot, while Andersen lost to Janowicz.
"Obviously it's disappointing to lose. We came to win," De Jager said.
"We were struggling under the circumstances - with Kevin (Anderson) not playing, Raven's injury and then Rik's back problem - but this is something we cannot control.
"We came here fighting and the team spirit was excellent."
While Poland will progress to the World Group playoffs, South Africa will fight to retain their place in Group One later this season.