A new and distinct nectarine tree variety, prunus persica var. `Sunectwentyone` that possesses a relatively low chilling requirement of 250 hours at or below 7.2.degree. C.; heavy production of relatively large (66 mm), very firm fruit that can be harvested about May 8-15 in Kern County, CA, (about 4 days after `April Glo` nectarine (U.S. Plant. Pat. No. PP7305)). The nectarine fruit is bright red with bright yellow flesh that is moderately juicy, very firm, and tart-sweet with 12 brix. The plant has a relatively low tendency for split-pits, russeting, and thrips damage.