India A rode on Shreyas Iyer's unbeaten century and all-rounder Vijay Shankar's half-century to thrash South Africa A by seven wickets and retain the tri-series trophy in Pretoria.Chasing a modest 268, Iyer with 140 not out and Shankar with 72 runs put on 141 runs for the third wicket to rescue the visitors from a precarious 20 for 2. Earlier, Farhaan Behardien with 101 not out and Dewald Pretorious with 58 runs helped the hosts recover from a disastrous 32 for 3 to post 267for 7.Brief Scores: South Africa A 267 for 7 India A 270 for 3