Cobus Reinach says he has grown as a player since switching to Saints.
The scrum-half scored on his South Africa return last Saturday, coming off the bench to round off a 35-17 success against Australia in the Rugby Championship opener in Johannesburg.
Reinach had not played for the Springboks since 2015, but his fantastic form for Saints earned him a recall.
The 29-year-old, who moved to Northampton from the Sharks in 2017, scored 17 tries in just 30 appearances in all competitions last season.
He was the joint top scorer in the Gallagher Premiership, alongside Sale wing Denny Solomona, and was named in the league's dream team.
Reinach also scooped both the supporters' and players' player of the year prizes at Franklin's Gardens.
And his fine form carried into international action as he grabbed a last-gasp score against the Wallabies last weekend.
"After disappointments like in 2015 (when Reinach missed out on World Cup selection) you take a step back and think what you can improve," said Reinach.
"Going overseas, you are definitely out of your comfort zone. You don't know their coaches, you don't know their structures or anyone around you so you're really out of your comfort zone at the beginning and you grow as a player."
Reinach will be desperate to book a ticket to the Rugby World Cup with the Springboks, but he has plenty of competition for the No.9 shirt.
Sale's Faf de Klerk is another hugely impressive performer, while the man who started last weekend, Stormers star Herschel Jantjies, scored twice against Australia
"I've seen him play quite a bit," said Reinach when asked about Jantjies.
"Like all of you can see, he's a quality player. We wouldn't have a player who's not good enough at this level, so everyone is good enough.
"He's had an unbelievable debut so hats off to him."