The 25-year-old has won two previous caps for his country following his debut two years ago.
Willian has now been given the chance to impress national team manager Luiz Felipe Scolari ahead of next year's World Cup in Brazil.
"I was always with expectation, hopeful, waiting for an opportunity," he told UOL. "Thank God it happened at this time and I was very happy."
Willian has scored one goal in 10 games for Chelsea since joining the Premier League club from Anzhi Makhachkala at the end of August.