CHICAGO -- The Pirates came to Chicago hoping to build off of the momentum they had established entering the All-Star break.

Instead, they will leave town on a three-game losing streak trying to find their footing and attempting to find a way to remain in the thick of things in the National League Central.

The Pirates, who had won 14 of 21 games to get to within 2 1/2 games of the Cubs entering the weekend, built an early lead on Sunday before starter Trevor Williams yielded three home runs -- including a pair on consecutive pitches in the sixth inning -- as part of an 8-3 loss to the Cubs, who completed the sweep at Wrigley Field.

• Box score

After losing ground on the first-place Cubs, the Pirates now head to St. Louis with another pivotal three-game series against the Cardinals beginning Monday night.

“When you play every day... [it’s about], ‘Stop this,’” manager Clint Hurdle said. “We need to find a way to create some more momentum and get some consistency back across the board with the pitching, the fielding and the hitting.”

Williams, who pitched for the first time since July 1 after coming off the paternity list during last week’s All-Star break, gave up a season-high eight runs and 11 hits over 5 1/3 innings. Williams got hit hardest in the fifth and sixth innings when the Cubs scored six times and got homers from Jason Heyward, pinch-hitter Albert Almora Jr. and Kyle Schwarber.

Almora and Schwarber connected on their solo shots on back-to-back pitches before Williams was pulled from the game. Williams struggled with fastball execution but wouldn't use his 13-day layoff as an excuse for his troubles, especially late in Sunday's outing.

“You just have to take it one pitch at a time and try and out-execute the other pitcher,” Williams said. “Today, [Cubs starter] José Quintana did that. Quintana won that battle.”

The Pirates built a 3-1 lead in the third inning when Bryan Reynolds delivered a one-out RBI single on Pittsburgh’s third straight hit of the frame. Starling Marte followed with a run-scoring sacrifice fly before Jung Ho Kang extended the lead to two runs with a double.

The Pirates, who were outscored 22-10 in the series, couldn’t add on, which Hurdle said will be one of the focal points moving forward. Kang, for one, isn’t worried after such a rough start to the second half.

“It’s tough, but the season is long,” Kang said. “You have to keep playing on and on.”

Williams agreed.

“Division games are worth more. They’re weighted more because you’re playing against [rivals] directly,” Williams said. “It’s a tough first series out of the break for us. However, we have an opportunity to go to St. Louis tomorrow and win the first one and go from there.

“We’ve got all of the confidence in the world in our guys. … Once we catch fire and we get going, we can be a really fun team to watch.”

The Cubs, who narrowed the gap in the fourth inning on an RBI single by Quintana, responded with three runs in the fifth to take the lead. Kris Bryant and Anthony Rizzo singled to start the inning before Victor Caratini tied the game at 3 with a sacrifice fly. Heyward then gave Chicago the lead with a two-run homer as the Cubs went on to score seven unanswered runs.

Despite the struggles of the past three days, Hurdle refuses to put too much emphasis on the skid.

“There’s a lot of things that are looked at differently externally than we look at them internally,” Hurdle said. “I don’t think you put more attention in any one area. We came in here with an opportunity to do something 2 1/2 [games] out, [and now] we’re 5 1/2 out. You just go. You go and get ready to play the Cardinals.

“These are men who know what’s at stake, who know how to prepare and know how to get ready.”