Nicholls, who used up two lives early in his innings, had a third on 92 when he was dropped by Azhar Ali and progressed to reach 100 with a cover drive to the boundary.
It took Rizwan just 60 deliveries to bring up his sixth half-century, fittingly reaching the mark with a boundary to underscore his aggressive approach despite the green wicket.
Alam had been discarded by Pakistan in 2009 after three Tests and a best innings of 168, and since his recall this year his highest score was 21 against England in August.
Alam clipped a ball just wide of Henry Nicholls at short leg, an attempted drive was edged just wide of an outstretched Tom Latham at gully, and one off the gloves fell just short of the cordon.
Azhar Ali was caught behind off an outswinger for five, and although the umpire initially said not out New Zealand sought a review which proved otherwise.