Nadal, who is playing his third clay-court event in four weeks since returning from a seven-month lay-off through injury, completed victory in an hour and 16 minutes.
Alund looked to be headed the same way as Nadal's first-round opponent Diego Schwartzman, who was dismissed 6-2 6-2, when he was served up a bagel in the opening set.
Nadal won an impressive 88 per cent of his first service points during that opening stanza and claimed three of seven break opportunities.
But credit to Alund - like Schwartzman, a qualifier from Argentina - he rallied in the second set and more than doubled the success rate on his own first service points from a meagre 31 per cent in the first to 65.
Alund managed to bring up three break points but, tellingly, failed to win any of them. Nadal was similarly wasteful however, having had five of his own and only converted one.
Crucially though, that one success was enough to seal victory, keeping alive the world number five's hopes of reaching a third final on his Latin American tour - he was runner-up in Vina del Mar before winning the Brazil Open title in Sao Paulo.
Nadal will now play Leonardo Mayer for a place in the semis after the Argentine downed Russian Andrey Kuznetsov 6-2 6-2.
Earlier, top seed David Ferrer continued his bid to defend his title with another comfortable victory, this time a 6-2 6-1 win over American qualifier Wayne Odesnik to reach the quarter-finals.
The world number four and three-times defending champion at the tournament, was in imperious form once again, dropping just three games on his way through. That is now just six games dropped from two matches.
He won 70 per cent of his second service points and has lost a total of just 11 points on his second serve in his Mexican campaign.
Ferrer, who remains on course for a potential final meeting with Nadal, moves on to meet Paolo Lorenzi in the quarters after the Italian saw off Pablo Andujar of Spain 6-4 6-3.
Nadal and Ferrer's compatriot Nicolas Almagro, the third seed, earned a 6-4 7-6(4) win over yet another Spaniard Tommy Robredo.
Acapulco International results
3-Nicolas Almagro (Spain) beat Tommy Robredo (Spain) 6-4 7-6(4)
2-Rafa Nadal (Spain) beat Martin Alund (Argentina) 6-0 6-4
Paolo Lorenzi (Italy) beat Pablo Andujar (Spain) 6-4 6-3
Fabio Fognini (Italy) beat Aljaz Bedene (Slovenia) 2-6 6-4 7-6(4)
1-David Ferrer (Spain) beat Wayne Odesnik (U.S.) 6-2 6-1
Leonardo Mayer (Argentina) beat Andrey Kuznetsov (Russia) 6-2 6-2
8-Horacio Zeballos (Argentina) beat Daniel Gimeno-Traver (Spain) 6-2 6-3
Santiago Giraldo (Colombia) beat Joao Sousa (Portugal) 7-6(8) 7-5