The world and European champions had 80% of the possession in the first period, but they could not make the breakthrough with Belarus compact in defensive areas.
The match followed a similar pattern in the early stages of the second half, but a thumping strike from Xavi moved Spain ahead just past the hour mark, before Alvaro Negredo made it 2-0 after 78 minutes.
Sergei Kornilenko had one back for Belarus in stoppage time, but it was a case of too little too late as the home side held on for a vital three points as they moved one step closer to booking their spot in the finals.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
SPAIN: Valdes; Arbeloa, Ramos, Pique, Monreal; Xavi, Busquets; Silva, Michu, Pedro; Fabregas
BELARUS: Gutor; Martynovich, Verkhovtsov, Bordachev, Filipenko; Dragun, Zhavnerchik, Putilo, Balanovich; Tigorev, Kalachev