SAN FRANCISCO -- Four days in August. They altered the 2015 season for the Chicago Cubs, taking their confidence to new heights. A sweep of the defending World Series champions will do that for a team, as the San Francisco Giants came to town the owners of three titles in the five past seasons. They left Chicago with the Cubs owning them. It was a sweep that changed everything for a young Cubs team.

"At that particular time it was in the middle of the summer," pitcher Jon Lester recalled earlier this week. "It definitely had some wild-card ramifications for us where if we dropped three out of four it could put us in a pretty big hole. We end up sweeping them, so I think on a confidence level for some of the young guys that really helped."

To review: The previous weekend, the Cubs had reached 10 games over .500 for the first time all season. It had been a grind to get there and, yes, they were feeling good about themselves. But they were far from a perfect team and what was to come in the fall was still a hope not a certainty. Still, things came together better that weekend than anyone could have imagined.

Game 1: Thursday, Aug. 6. Final: 5-4

The Cubs shot out to a 5-0 lead after two innings, thanks in part to Kyle Schwarber's three-run blast in the second inning off Giants starter Chris Heston. But the win wouldn't come easy as those were the last runs the Cubs would score, while starter Jason Hammel was surprisingly pulled by Joe Maddon after just four innings and a 5-2 lead. For the first time all season the Cubs manager showed a sense of playoff contending urgency.

"We took Jason out a little early that one game," Maddon explained. "Paradigm shift."

It was as if Maddon was telling his team a nice run to 10 games over .500 wasn't enough. He wanted more -- and he got it.

"Obviously, whenever you get the world champs coming in you want to elevate your game," Hammel said. "When the best arrive you want to make sure your best is there for that game or series. It was a huge moment for us. A momentum builder. Almost a confirmation to ourselves that we were that good."

At the time Hammel bristled at being taken out early but he was more than happy the Cubs held on as closer Hector Rondon sealed the deal with a one-two-three ninth inning.

Game 2: Friday, Aug. 7. Final: 7-3

The day before would mark Starlin Castro's last game as the Cubs' starting shortstop. His season-long slump had dropped his batting average to .236 after a 0-for-4 day. Meanwhile Addison Russell's ascension had taken on a new feel. The leg kick he added during the All-Star break produced more gap power. He began driving the ball more and more in the second half and the Cubs simply believed they would be a better team with him back at his natural position. By Friday, the job at shortstop was all his.

"Yeah I remember it well," Russell said. "Switching over to shortstop. Just had a brand-new son at that time too. First game of the series after being at the hospital for four days. It was awesome to come back to that atmosphere."

Russell went 1-for-4 in Game 2, scoring a run as part of a five-run fifth inning that cemented the Cubs' second straight win. Rookies Jorge Soler and Schwarber drove in two runs apiece in the fifth and once again Maddon displayed urgency in calling on Rondon for a two-inning save.

"If you look at their team they were really good from top to bottom," Russell said. "Sweeping a team like that is not easy and we just took off from there."

Game 3, Saturday, Aug. 8. Final: 8-6

Game 3 was a see-saw affair, which saw scoring by one team or the other in all but two innings. Kris Bryant's two-run home run in the third off of Matt Cain gave the Cubs a lead they'd lose, but two more runs in the fifth put the Cubs in front for good -- though they needed the three runs they scored in the eighth inning to win the game.

That was because it took three pitchers to get the Cubs through the ninth inning, as Rondon was unavailable due to his usage in Games 1 and 2. Justin Grimm earned the save just two days after getting the series-opening victory entering the game in the fifth inning. That's Maddon at his finest: One day Grimm was a middle man, two days later he's finishing off the Giants. But not before three Giants runs had crossed the plate and the tying run was standing in the batter's box, but Matt Duffy grounded out to end the drama.

"Every game felt like that," Russell stated. "We played up to the atmosphere and the hype. That series had all of that."

Lester added: "We also lucked out a little bit. We caught them at a pretty good time. They had some injuries and we played some really good baseball that week and I feel like that kind of set us up for later in the year."

Game 4, Aug. 9. Final: 2-0

The fourth game is the one remembered best by players, because somehow the two runs the Cubs scored in the first two innings off of Jake Peavy held up. The Giants were mostly stifled by Jake Arrieta that afternoon as he was just starting his run of dominance that continues to this day. But after 117 pitches he gave way to Grimm and then Rondon, who would walk a tightrope for his 19th save.

"I remember that last game," Lester said. "The ninth inning."

A near capacity crowd had their brooms out for the sweep but not before Rondon loaded the bases as Brandon Belt singled, Brandon Crawford doubled and Ehire Adrianza was hit by a pitch. Rondon was in meltdown mode.

"We realized when we play our game, no matter who it was against, if we compete we have a chance," Lester said. "I think that carried over throughout the rest of the year for us."

But then Rondon got pinch-hitter Hector Sanchez swinging. One out.

"That ninth inning was something else," Russell said. "Bases loaded, nobody out. I remember that well."

Former Cub Angel Pagan also went down swinging, though it took eight pitches. Two outs.

"Momentum in sports is everything," Hammel said. "Anytime you can do that and look back on it, it was like ‘wow.'"

Giants outfielder Gregor Blanco would last one pitch longer than Pagan. In perhaps the most dramatic moment to that point in the season, Rondon threw three pitches to Blanco with a full count. Three times the runners started, twice the hitter fouled the ball off. But Blanco took the ninth pitch of the at-bat, a slider, for a called strike three. The sweep was complete.

"I remember that last game," Fowler said. "I remember Rondon striking out Blanco with the bases loaded. That was fun."

The Cubs surged to 14 games over .500 and would win five more consecutive games after that. It wasn't necessarily the turning point to the season, but it definitely was the coming out party for a new contender in baseball.

"Maybe we had no business winning those games, but you get a bunch of guys with some innocence of being up in the big leagues and doing their thing we molded and formed as a team in that series and opened some eyes," Hammel said. "It set the tone."

On Friday, Arrieta is on the mound against the Giants, just as he was in that finale last August. This time the Cubs are on the road, where they've fared pretty good so far this season. The Cubs Cy Young winner was a little less nostalgic about the series last year than his teammates as he was focused on the current task at hand.

"New series, new team, new year," Arrieta said Thursday morning. "We're tough to beat. They're good too. We're going to be ready."