However, Hammel was frustrated about being taken out early. He pitched six-plus innings, and Justin Ruggiano homered for the second straight game, leading the Cubs to a 7-2 victory over the Washington Nationals.
The teams reached agreement on a deal that would send Samardzija and Hammel to Oakland for three top-line prospects in a surprising trade by baseball's top team two people with knowledge of the deal said Friday night.
The people, who spoke to The Associated Press on condition of anonymity because the deal was still pending, said the A's will send top prospect Addison Russell, outfielder Billy McKinney and pitcher Dan Straily to the Cubs. An official announcement will likely not happen until Saturday.
The trade is a rare move under general manager Billy Beane in which Oakland - one of baseball's most frugal franchises - parted with talented young prospects for proven players to chase a World Series title. The A's are a major league-best 53-33 after beating Toronto 1-0 in 12 innings Friday.
Hammel's outing on Friday was cut short, for unknown reasons. Samardzija had been scheduled to start against Washington on Saturday.
Chicago was leading 4-1 when Hammel was pulled after Anthony Rendon hit his 92nd pitch for a leadoff double.
''I would have liked to have stayed out there in the seventh,'' Hammel said. ''I have no idea why I came out of the game. I honestly believe you learn how to pitch when you get to 100 pitches. If you're not allowed to reach that, I think that's hurting you more than helping.''
Hammel has gone over 100 pitches in eight of his 17 starts, including his previous two outings.
''All I can say is it's frustrating, especially when you feel good,'' he said. ''Quite honestly there's no reason for me to go back out there if I'm just going to give up the runner and then (get) pulled.''
Cubs manager Rick Renteria said of the move: ''Go ahead and make a change there and not let him get into a situation.''
Neil Ramirez then struck out Ian Desmond before Wilson Ramos singled home Rendon to make it 4-2. Ramirez retired the next two batters to limit the damage.
The Cubs broke it open in the ninth when Ruggiano singled in Darwin Barney, and Starlin Castro added a two-run single.
Ruggiano connected for a solo shot against Tanner Roark (7-6) in the third inning. He has seven RBIs in his last two games and is batting .444 (12 for 27) in his last seven games overall.
''Hitters go through this every now and then,'' he said. ''You get hot, seeing the ball well. I've been doing some things mechanically to stay on top of what I want to do at the plate. It's good though, I don't want to lose it.''
Chris Coghlan had two hits and scored three times as the Cubs had 14 hits in their fourth consecutive victory.
Hammel was charged with two runs in his second consecutive victory against Washington. The 6-foot-6 right-hander allowed two runs in 6 1-3 innings in a 7-2 victory over Roark and the Nationals on June 27 in his previous start.
Hammel, who also had an RBI single in his latest victory, improved to 8-0 with a 3.11 ERA in 10 career starts against Washington.
The first two Nationals reached in the fifth, but Hammel recovered from a 3-0 count to fan Roark attempting to bunt.
''That was huge,'' he said. ''I couldn't find the strike zone. I was overthrowing.''
Denard Span then grounded into a fielder's choice, and Bryce Harper struck out.
Jayson Werth homered in his second straight game and added a double for the Nationals, who had won five in a row.
Roark was charged with four runs and nine hits in seven innings in his second straight loss after a personal four-game winning streak.
''They did what they did last time - base-hit me,'' he said. ''Got beat.''
NOTES: Werth is 6 for 10 with two homers, three doubles and six RBIs in his last three games. ... Chicago's Nate Schierholtz, running from first on a pitch in the fourth, took a step past second base on John Baker's fly out to center. When he didn't retouch second on his way back to first, the Nationals appealed and Schierholtz was called out. ... The last time starters with identical records and ERAs with at least 15 starts squared off was August 15, 1974, when Jim Kaat of the White Sox opposed Baltimore's Mike Cuellar. Both pitchers then were 13-9 with a 3.54 ERA.
AP Baseball Writer Janie McCauley and AP Sports Writer Antonia Gonzalez in Oakland and AP Sports Writer Jay Cohen in Chicago contributed to this report.