Belt slugged his fifth homer of the young season and finished 2-for-4 with a pair of RBI, while Pagan went 2-for-3 with two runs scored to raise his average to .441.
Hudson (2-0) impressed as well in his first AT&T Park start as a Giant, with the offseason pickup yielding three runs -- two earned -- and not walking a batter to beat Arizona for the second time in five days.
Michael Morse and Brandon Crawford also had two hits and a pair of RBI for San Francisco, which owns a National League-best 6-2 record at the moment.
Arizona, on the other hand, fell to 2-8 and got a shaky outing from starter Trevor Cahill (0-3), who lasted just 3 1/3 innings and was tagged for five runs and eight hits.
Martin Prado recorded three of the Diamondbacks' seven hits on the afternoon.