Back-to-back homers by Nick Martini and Marcus Semien in the eighth inning brought the Oakland A's to within a run of the Chicago Cubs, but that's as far as they could get in a 6-5 loss at Wrigley Field.
Javier Baez hit two of Chicago's four homers and the Cubs' bullpen barely held on without Craig Kimbrel, closing out the victory.
Ian Happ and Nicholas Castellanos also connected as Chicago improved to 40-18 at home with its fourth straight win. It was Castellanos' first homer since he was acquired in a trade with Detroit on Wednesday.
The Cubs are counting on their depth to help them stay on top of the NL Central until Kimbrel and Willson Contreras return from injuries. Kimbrel was placed on the 10-day injured list before the game with right knee inflammation, and Contreras is expected to miss four weeks after an MRI showed a Grade 2 hamstring strain.
Manager Joe Maddon said it will be closer by committee while Kimbrel is out, and Victor Caratini will be the primary catcher while Contreras is sidelined. The 12-hit attack in the series opener helped make up for Contreras' absence, but the bullpen was an adventure - right until the very end.
Oakland had won six of seven and nearly pulled off an impressive rally in its first game at Wrigley Field since 2010. Marcus Semien went deep twice for the A's, and Nick Martini connected for his second career homer in a successful homecoming for suburban Chicago native.
The A's had two runners on with two out in the ninth when Semien came up just short in his bid for a third homer, flying out to the warning track in left-center.
Phelps, who came in after Kyle Ryan faltered, earned his first save since he came over in a trade with Toronto last week. Rowan Wick (2-0) got two outs for the win.
The game was tied at 2 when Happ opened the seventh with a pinch-hit drive off Blake Treinen (5-2) that traveled an estimated 474 feet to right-center. It was Happ's first major league homer since Sept. 14 against Cincinnati.
Castellanos added an RBI double and Baez belted a two-run shot as Chicago opened a 6-2 lead. Baez also hit a tying solo drive off Chris Bassitt in the sixth for his 27th homer.
The A's responded with three in the eighth on consecutive homers by Martini and Semien off Steve Cishek. They had runners on the corners with two outs when Brandon Kintzler retired Mark Canha on a sharp grounder to second.
The high-scoring finish was a marked contrast to the solid performances for starters Bassitt and Kyle Hendricks.
Castellanos put Chicago in front with an opposite-field drive to right in the first. He is batting .400 (8 for 20) in five games with the Cubs.
Hendricks allowed just one hit in 6 1/3 innings - and it was a big one. With two out in the third and Jurickson Profar aboard after a leadoff walk, Semien drove a 2-1 pitch deep to right for his 18th homer.