Djokovic, the world No. 1, remained on track in his bid for a third straight Miami championship with a 6-2, 6-4 decision over India's Somdev Devvarman.
The Serbian superstar's triumph was his 14th consecutive at Crandon Park.
Spain's Ferrer gained the Round of 16 with a 6-1, 7-5 win over 32nd-seeded Italian Fabio Fognini.
In other matches Sunday, No. 7 Janko Tipsarevic of Serbia got past 26th-seeded Kevin Anderson of South Africa 4-6, 7-6 (7-5), 6-0 and 11th-seeded Gilles Simon of France dispatched Slovenia's Grega Zemlja, 6-4, 6-4.