The Cubs dealt the infielder to the Giants about two hours before the two teams met in the third game of a four-game series for Minor League outfielder Evan Crawford. The Giants placed Edgar Renteria on the disabled list prior to Wednesday's game.
Cubs assistant general manager Randy Bush said talks began before the Trade Deadline. General manager Jim Hendry was in Minneapolis on Wednesday for the owners meetings and completed the deal with Giants general manager Brian Sabean there.
The Cubs so far have dealt infielder Ryan Theriot and pitcher Ted Lilly to the Dodgers on July 31 and now Fontenot.
"Anything we can do that we feel is to the betterment of the organization, we'll continue to look," Bush said. "It's hard to say if it will be the last move."
Fontenot, who was the Cubs' Opening Day second baseman, was batting .284 with one home run and 20 RBIs in 95 games, but his playing time had been reduced since early May. At that time, the Cubs called up Starlin Castro from the Minors and inserted him at shortstop, moving Ryan Theriot to second. Fontenot was out of a job.
"It's strange, being in the same town that you're traded to," Fontenot said. "I was telling someone I was trying to decide if I was going to work out or get a bite to eat and I was called into the office and told I was being traded."
"He's got a short little walk," Cubs acting manager Alan Trammell said. "I told him to take it easy on us. It's a good opportunity for Mike to go to a team that's in contention."
He was wearing a Cubs T-shirt and shorts when he got the news, changed into his street clothes and then walked down the hallway at AT&T Park to the home clubhouse where he got settled. He'll wear No. 14 with the Giants. Aubrey Huff has No. 17. The good news for Fontenot is that he will be reunited with another LSU buddy, Giants closer Brian Wilson.
The Cubs will call up infielder Darwin Barney from Triple-A Iowa to take Fontenot's spot on the roster and try to get him in San Francisco in time for the series finale Thursday. Barney has played the majority of games at shortstop at Iowa, where he was batting .297 with two homers, 24 doubles and four triples. Welington Castillo made his Major League debut Wednesday night and is the 14th rookie to appear in a game for the Cubs this season. Barney would be the 15th; the club record is 17 set in 1902.
"Mike Fontenot was a very good teammate and his teammates liked him very much," Trammell said. "As we know, what happens when you're losing is changes are made."
The Cubs players joked that they were going to put Fontenot into one of the laundry hampers and roll him down the hallway to his new team. He does pick up a few games in the standings.
"I'll do my best to help them," he said of the Giants.
Fontenot kept a good outlook despite losing his starting job.
"It's been tough in that aspect but as far as my performance, I've been pretty happy," Fontenot said. "There have been times when I would have liked to get out there and play more but I've always been a team guy. Things didn't go the way we wanted to early in the season. In the end, I felt pretty good this year."
Crawford, 22, was selected by the Giants in the ninth round of the 2009 First-Year Player Draft. He was batting .255 with 12 doubles, 12 triples, four home runs and 24 stolen bases for Class A Augusta.
Instead of going to St. Louis this weekend with the Cubs, Fontenot will stay in San Francisco.
"I'm glad I packed a few more long sleeves [shirts]," he said. "It's going to be different but I'm excited for the change."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.