"We needed this win. I blew the win tonight and I have to live with it," said Robertson, who was saddled with the blown save and his first loss of the season.
He came on with two away in the eighth to retire Russell Martin, sending the White Sox into the ninth with a 9-7 lead. After Chicago came up empty in the top half, Blue Jays No. 9 hitter Josh Thole started the bottom of the ninth with a single -- his third hit of the game -- to give Toronto a baserunner. Jose Reyes then doubled, setting the table for Donaldson's walk-off.
"Fastball away," Robertson, who's 3-1 with nine saves on the season, said of the fateful pitch. "It caught a little too much middle and he put a great swing on it and it's just a good hitter doing a good job."
Robertson, who hadn't pitched since May 22, has been mostly untouchable this season. The right-hander had surrendered only two earned runs over 18 1/3 innings prior to Tuesday's outing.
White Sox manager Robin Ventura said his faith isn't shaken in his closer, and he expects Robertson will make an immediate bounce-back.
"It's a tough position. Closers are not for the faint of heart," Ventura said. "He's been doing it a long time. He'll be able to bounce back. This proves the guy's human, but he's been great for us.
Jamie Ross is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.