The world number five and second seed, gunning for an eighth Barcelona title, will face Paire on Friday morning with either sixth seed Kei Nishikori or Albert Ramos waiting in the next round should Nadal avoid an upset.
Third seed Tomas Berdych was also frustrated by the weather and will play his third round against Spaniard Tommy Robredo on centre court on Friday.
Before the weather intervened Russian qualifier Dmitry Tursunov, who shocked top seed David Ferrer on Wednesday, was ousted by 16th-seed Thomaz Bellucci 4-6 6-1 6-3.
Fourth seed Nicolas Almagro and seventh seed Juan Monaco will clash in the quarter-finals after straight set victories over Marcel Granollers and Jeremy Chardy respectively.
Barcelona Open results
4-Nicolas Almagro (Spain) beat 15-Marcel Granollers (Spain) 6-3 6-4
16-Thomaz Bellucci (Brazil) beat Dmitry Tursunov (Russia) 4-6 6-1 6-3
7-Juan Monaco (Argentina) beat 10-Jeremy Chardy (France) 6-0 7-6(11)
Bucharest International results
1-Janko Tipsarevic (Serbia) beat Santiago Giraldo (Colombia) 6-3 6-3
Guillermo Garcia-Lopez (Spain) beat Sergiy Stakhovsky (Ukraine) 1-6 6-3 6-4
Victor Hanescu (Romania) beat 4-Mikhail Youzhny (Russia) 6-4 6-3
5-Florian Mayer (Germany) beat David Goffin (Belgium) 7-6(2) 1-6 6-3