Manager Matt Williams pulls Gio Gonzalez from the game in the fifth inning. (Thearon W. Henderson/Getty Images)

Shortly before Christmas in 2011, the Washington Nationals traded away four top prospects to the Oakland Athletics for all-star Gio Gonzalez. Much has happened since — Gonzalez has cemented himself as one of the better left-handed starters in baseball, and some of Oakland’s players from the deal have contributed to two American League West titles.

Sunday, however, marked the first time some of the key figures in the deal met on the field, and Gonzalez’s former team had its way with him.

On a sun-splashed afternoon at Coliseum, Oakland handed Gonzalez a 9-1 loss to complete a three-game sweep. Oakland catcher Derek Norris, a rising prospect in the Nationals organization before being included in the six-player deal, did most of the damage with a pair of three-run homers.

“It’s always nice to come back to Oakland and see some familiar faces,” Gonzalez said. “But I still got a job to do and go out and pitch. Obviously it was a different story [Sunday].”

Norris, who was ranked the Nationals’ ninth-best prospect at the time of the trade, took extra satisfaction in beating Gonzalez.

“Most definitely and against the guy I was traded for,” he said. “It’s not that they don’t want you, but it’s always nice to stick it to them. They needed starters, and the A’s were looking for younger guys to fill shoes. It was a good place for me to break into the big leagues. I got a great opportunity when I was traded here.”

The Nationals have made a habit of falling behind early, and Gonzalez dug them a 4-0 hole in the first inning thanks to Norris’s first homer. Gonzalez took the mound Sunday afternoon to a nice round of applause from the home crowd but left in the fifth inning with his head down and his team facing a large deficit. His day was so frustrating that, after giving up Norris’s second home run in the second inning, television cameras showed an animated Gonzalez slamming his glove in the dugout and being restrained by pitching coach Steve McCatty.

It was unclear at whom Gonzalez was directing his anger.

“It’s just competition,” Manager Matt Williams said. “We’re not going to go any further than that with it. That’s the team’s business and for nobody else. But everybody wants to do well, and everybody wants to win.”

Added Gonzalez: “Nothing happened.”

Gonzalez appeared to have been upset about plays behind him in the field, including a foul pop by Yoenis Cespedes in the second inning that fell between three Nationals. Gonzalez went on to walk Cespedes, sending Norris to the plate with two runners on for the second time in as many innings. Neither time worked out well for the left-hander.

“You’re going to make a mistake,” catcher Jose Lobaton said. “That’s how we learn. That’s how we keep working. He got upset about that. . . . It’s a game that you’re going to make a lot of mistakes. It’s baseball. It’s over now.”

The Nationals entered Sunday with an .805 OPS, the fourth-best mark in the majors, against left-handed pitching. But they had nothing against veteran Scott Kazmir, who set down 15 straight at one point and yielded just four hits over seven scoreless innings.

As strong as Kazmir was, Gonzalez’s inability to get Norris out defined the game.

Sporting a unkempt beard, Norris stepped into the batter’s box in the first with Gonzalez struggling with his command. The left-hander missed with a first-pitch curveball and then two fastballs. Gonzalez needed a strike and left a fastball over the plate. Norris, hitting .385 in 78 at-bats, swung and drilled the pitch into the seats above the left field scoreboard.

As Norris ran around the bases, his wild hair flailing under his helmet, Gonzalez angrily gripped a new baseball and clenched his jaw.

A similar scene between Norris and Gonzalez unfolded in the second after the misplay on Cespedes popup.

“Could it have been a catch?” Williams said. “Potentially. But from Gio’s perspective, he didn’t throw enough strikes. And from our offensive perspective, we didn’t get enough hits. And that’s the bottom line of the game. Regardless of play or ball falling in or not, that’s not my concern.”

Gonzalez again fell behind 3-0 in Norris’s second at-bat. Again, he came with a fastball — and again Norris hammered it. Lobaton didn’t think Norris would swing at the first 3-0 fastball, but he knew it might happen a second time. He called a fastball in, and Gonzalez left it over the plate. The Athletics don’t often swing at 3-0 pitches, but Norris did twice.

“A 3-0 fastball down the middle: Would you wait for that pitch especially with men on base?” Gonzalez said. “I would have done the same thing.”

Former Athletic Jerry Blevins also faced his former team, pitching the seventh inning and only adding to the Nationals’ headaches. He walked a batter and allowed two doubles, pushing the Nationals’ deficit to 9-0. The Nationals scored one run in the ninth inning to avoid a second shutout at the hands of the Athletics.

The Nationals have benefited from the power of Gonzalez’s left arm over the past two-plus seasons, but on Sunday, the other half of the blockbuster trade got the better of him.