The co-head of Weil, Gotshal & Manges’ antitrust and competition practice became the firm’s first witness Monday in a legal malpractice trial. The case, in which opening statements were also delivered Monday, stems from Weil Gotshal’s representation of a New Jersey mall boutique in an unfair competition suit against Italian fashion house Fendi.

Annette and Randi Fischer, owners of Fashion Boutique of Short Hills, which sold Fendi goods, claimed Fendi instructed its Manhattan store employees to disparage the New Jersey store’s offerings, contributing to its 1991 closing. A federal jury awarded the boutique a disappointing $110,000 in damages in 2000. After Weil Gotshal sued the Fischers in 2003 for legal fees, the former owners counterclaimed for malpractice on the grounds the firm had a conflict of interest because Prada, which acquired an interest in Fendi in 1999, also became a firm client.