Sunday's defeat also sealed only the fourth sweep of Oakland in 2014.
"Good teams go through tough stretches in 162 games," Freiman said. "I'm confident that this is a tough enough group that is going to respond well, go home, have an off-day, and we'll get back to work."
The Athletics and the Angels remained tied for first in the American League West, with only four days remaining until the first of their final 10 games against each other down the stretch on Friday night in Oakland.
"That's obviously a good thing, a positive of it," Lester said of the Athletics still holding onto first place. "We've got to take all the positives we can right now and continue to grind. That's all we can do."
If the A's have plans of winning their third consecutive AL West title, they will need better offensive performances than the one they gave in support of Lester.
Oakland finished 0-for-5 with runners in scoring position, stranding Coco Crisp after a leadoff double in the first and Jonny Gomes after he reached second on an error with one out in the sixth. Gomes was stranded 180 feet from home when Josh Donaldson and Derek Norris both struck out looking to end the inning. The Athletics also erased baserunners in the fourth and the fifth by hitting into double plays.
"We're just coming up a little short," A's manager Bob Melvin said. "Unfortunately, that's where we are right now."
Lester gave up four runs (three earned) in six-plus innings against Atlanta. Going back to his time in Boston, Lester has recorded 12 straight quality starts, compiling a 7-1 record, a 1.67 ERA and a 0.95 WHIP in those outings.
The unearned run came courtesy of an errant throw by Donaldson, who otherwise had a stellar defensive night, snagging liners and scooping up several grounders with tricky hops.
One of those liners came off the bat of Chris Johnson following a Justin Upton single in the bottom of the second. Donaldson attempted to double off Upton, but his throw hit the Braves' left fielder in the backside and rolled away.
Upton advanced to third as the ball dribbled into the Atlanta dugout, and then scored when Evan Gattis lined a single into right field.
"Well, it's two bases, but I was kind of begging," said Melvin, who went out on the field to discuss the play with the umpires. "Just if he's going back to the base, I was seeing if you could try to keep it at one, but it's just not going to be the case."
The run negated a home run hit by Freiman off Minor in the top of the second that gave the A's a 1-0 lead. Freiman went deep again in the top of the seventh. Freiman has three homers in his past eight plate appearances after hitting only one in his first 43 plate appearances.
"At the end of the day, we do what we do to try to help the team win," Freiman said. "I was happy to be able to contribute a little bit, but ultimately, I'm here to help the team win, and unfortunately, we didn't win. It was nice to take some good swings, do some stuff to contribute, but it's going to be tough to leave a good taste in our mouths after being swept."
Freiman's blasts could not overcome the long balls surrendered by Lester, who gave up a two-run homer to Upton in the third and a solo shot to Johnson in the seventh.
Lester not only gave up more homers on Sunday night than he had in his previous 11 starts, but he surrendered multiple home runs in an outing for only the third time this season and for the first time since June 7.
"Sometimes, you've got to tip your hat," Lester said. "Sometimes they have a better game plan than you do, and they execute what they're trying to do."
Oakland added a run in the eighth on a sacrifice fly by Crisp, but was held scoreless by Braves closer Craig Kimbrel in the ninth as the Athletics suffered their seventh defeat in the past eight games.
"Guys are competing, we're just not getting results right now," Lester said. "The times that we need to get a guy in, we're just not doing it. The times we need to make a pitch, we're not doing it. This team's too good to stay in this funk."