MILWAUKEE — The San Francisco Giants are deep in discussions with Gary Pettis to fill their third-base coach vacancy, a team source told The Athletic on Monday.Pettis, 68, would replace Hector Borg, who was reassigned Friday after a series of questionable decisions to send or hold runners. Longtime Giants emeritus coach Ron Wotus coached third on an interim basis over the weekend at Coors Field and is expected to continue in that capacity for most, if not all, of the remaining trip.Wotus did not wish to return to a full-time position on the coaching staff.Pettis, an Oakland, Calif., native, would bring major-league experience the Giants had lacked with their on-field coaching personnel. Both Borg and first-base coach Shane Anderson were on a major-league coaching staff for the first time while serving under first-year manager Tony Vitello.It’s also a good bet Pettis comes highly recommended from two respected former managers inside the Giants organization.The former five-time Gold Glove center fielder has served as a major-league coach for 25 seasons with five organizations, including 2015-24 with the Houston Astros when he overlapped for a time under Dusty Baker, who is currently a Giants special assistant. Pettis also coached from 2007 to 2014 with the Texas Rangers under Ron Washington, who is San Francisco’s infield coach.