The Barcelona attacker scored a superb treble for Vicente Del Bosque's side, as Spain put in a fine performance to secure all three points and make it two wins from two in Group I
La Roja could have been two goals up within four minutes of this match, as Cesc Fabregas saw an effort from a tight angle deflected on to the post, while David Silva wasted a glorious chance seconds later by shooting into the side netting, after he had latched on to a divine lobbed through-ball from Xavi.
It did not take La Roja long to take the lead however, as Alba made it 1-0 in the 12th minute following a wonderful move involving Xavi and Pedro. The young fullback passed inside to Xavi, who then rifled a low ball into Pedro. The attacker had his back to goal but somehow flicked an unorthodox pass through to the overlapping Alba who had continued his run. The Barcelona left back took the ball in his stride in what looked to be an offside position, dribbled past the Belarus goalkeeper Sergei Veremko, and then slotted the ball into the empty net for his second international goal.
Pedro increased Spain's lead 10 minutes later, dinking a neat shot past Veremko area after being set up by an inch-perfect through-ball from Silva. The Barcelona man did brilliantly to shift the ball out of his feet after receiving Silva's pass on the edge of the Belarus box, before chipping a deft effort over Vermeko and into the back of the net.
Silva continued to act as Spain's creative hub as the first half wore on and Vicente Del Bosque's side continued to control the game. The Manchester City attacker came close to providing his second assist of the evening, after nut-megging Pavel Plaskonny on the right-hand side and drilling a low pass across the six-yard box that Fabregas was inches away from diverting past Veremko.
Spain started the second half in a similar vein to how it finished the first, and may well have added a third goal but for a superb block from Aleksandr Martynovich. The defender deflected Pedro's cross behind for a corner from in front of his own goal, as Fabregas lingered behind him waiting to connect with the pass.
The home side showed more attacking intent after the break but continued to struggle in creating goalscoring opportunities, and Spain made them pay for committing men forward by hitting them on the counterattack to score a third in the 69th minute.
Xavi provided a masterful assist for the goal, taking four defenders out of the game with a sumptuous through-ball that Pedro raced on to before dispatching another looping effort over Veremko and into the far corner of the net from just inside the penalty area.
Within minutes of the third Spain had a fourth, with Pedro completing his hat trick with a close-range finish after some calamitous defending from Belarus. A woeful touch from Martynovich allowed Fabregas to steal possession on the left, and he wasted no time in playing the ball in to Pedro, who flipped the ball over the onrushing Veremko before passing the ball into the empty net.
Belarus had a chance to reduce the deficit in the 76th minute through Stanislav Dragun, but he fired wastefully over Casillas' crossbar after being put clean through by Sergei Kislyak.
Spain's substitute David Villa nearly added a fifth for his side late on, but the Barcelona forward could only watch on in despair as his powerful effort from 15 yards came crashing back off the crossbar.
The victory means it is two wins in two matches for Spain in Group I, with France its next opposition on Tuesday. Belarus, meanwhile, has lost all three of its matches so far, and faces Georgia next.