The 27-year old Japan international followed up his match-winning brace against Eintracht Braunschweig last month by netting in the 17th and 70th minutes as Mainz swept to a three-goal lead.
Nicolai Muller opened the scoring inside seven minutes before Okazaki doubled the lead when he volleyed home from the six-yard box after a deflection off the crossbar.
The former Stuttgart man then grabbed his fifth league goal of the campaign when he slotted home Stefan Bell's low cross from close range before Eljero Elia and Franco Di Santo grabbed late goals for Bremen.
The victory sees Mainz move up to seventh on the table while Okazaki joined a host of players on five goals to sit equal fifth on the scoring chart.
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