[1] After having a standout career as a high school player at East Chicago Washington High, while playing for head coach Johnny Baratto; Mantis enjoyed a stellar collegiate career at Northwestern, where he led the Wildcats in field goal percentage as a senior.

That season (1958–59), he served as team captain, and led them to their best finish in the Big Ten - a tie for 2nd with an 8–6 conference record, 15–7 overall.

The Wildcats won nine of their first ten games, dropping a stunner to #5 ranked North Carolina in the University of Louisville-hosted 'Bluegrass Festival Tournament.'

The Wildcats spent seven consecutive weeks on the AP Poll, and knocked off the Jerry West-led West Virginia Mountaineers.

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