The Cherries rang the changes after last week's loss at Arsenal, with skipper Simon Francis one of those to come in, while Liam Rosenior was included for the Seagulls in place of the injured Bruno.
A lack of quality was a feature of the early stages, with the hustle and bustle on show not matched by quality.
Anthony Knockaert and Charlie Daniels both tried their luck from distance, while Davy Propper went close with a cute effort from the edge of the area.
However, the best moment of the opening half came when Defoe turned brilliantly before striking goalwards, only for his dipping effort to go wide.
The second half almost started with a bang when Brighton's Shane Duffy had a header cleared off the line by Andrew Surman, before Dale Stephens nodded another Duffy effort onto the bar.
They now had the bit between their teeth and got their reward soon after when Solly March made the most of more poor defending to nod home Pascal Gross' wonderful cross.
That sparked Bournemouth into life and the introduction of Jordon Ibe on 65 minutes paid dividends when after receiving the ball from Surman, he produced a delightful backheel in returning the favour to his colleague.
Surman still had work to do but finished with aplomb, coolly dropping his shoulder to outfox Lewis Dunk, before slotting home.
Ibe himself then went close and repeated his magic soon after, finding Defoe in the area and the England man fired in to make it 2-1.
That left 17 minutes for Brighton to hit back but they failed to create any real chances and the Cherries sealed their first win of the season.