Denílson gained more than 60 caps for Brazil, making his full debut before his 20th birthday and representing the nation in six international tournaments, including two World Cups (winning the 2002 edition).

[2] He made his La Liga debut on 29 August in a 0–0 away draw against Alavés,[3] and finished his first season with 35 games and two goals as his team ranked in 11th position; the Andalusians were relegated to Segunda División in 2000.

In 2004–05 Betis finished in fourth position and qualified to the UEFA Champions League, also adding the season's Copa del Rey, but Denílson was only a fringe player now, starting in just three games and playing only 290 minutes.

Further fueling speculation, head coach Steve Morrow said the player would need to "earn a spot in the starting lineup like everybody else"; goalkeeper Darío Sala added the team was having problems adjusting to a change in scheme to accommodate Denílson.

He was unable to make the starting squad, spending most of the season as a bench option; nonetheless, he helped Verdão to the São Paulo State Championship and a berth in the Copa Libertadores after the fourth place in the Série A.

[13] He made his debut on the 21st against Hoàng Anh Gia Lai, scoring through a free kick just two minutes into the game, but left after only three weeks with the team with only that single appearance to his credit due to injury.

[15] A creative and technically gifted left-footed player, Denílson usually played as a left winger either in midfield or up-front, and was mainly known for his pace, flair, and dribbling skills, in particular for his use of several tricks and feints to beat opponents, such as the step over, which he frequently employed;[16][17][18][19][20] however, he was also infamous for his inability to score consistently in front of goal, and for his tendency to pick up bookings.

In a global advertising campaign in the run-up to the 2002 World Cup in Korea and Japan, he starred in a "Secret Tournament" commercial (branded "Scorpion KO") directed by Terry Gilliam, appearing alongside football players such as Fabio Cannavaro, Hernán Crespo, Edgar Davids, Rio Ferdinand, Luís Figo, Paul Scholes, Thierry Henry, Gaizka Mendieta, Hidetoshi Nakata, Ronaldinho, Ronaldo and Francesco Totti, among others, with former player Eric Cantona the tournament "referee".