Whereas Parker initially found trouble in a four-hit second inning, Weaver limited Oakland to four hits through nine shutout innings on Monday, en route to capturing a 4-0 victory, marking his 10th straight win and Major League-leading 15th of the season.
"It was one of those things where I didn't feel too good in the bullpen, but was able to figure something out when I got out there," Weaver said.
The A's never did, and they have been shut out 13 times this season, most in the Majors. Moreover, they've dropped three straight and five of their past seven, that July magic suddenly dissipating.
They're subsequently back in third place in the American League West, having also passed top Wild Card holder honors to the Tigers with the defeat. It's the Angels, who had dropped four of their previous five games, who return to second place behind Texas.
The Halos were just 20-25 when they last faced the A's in May, when Oakland's ledger read 22-23.
Parker has played a key role for the A's in that regard, though the righty has allowed at least four runs in four of his past six starts for a 5.95 ERA over that span. On Monday, the rookie too often found himself in hitters' counts and was subsequently offering up one too many pitches to hit.
Nine found holes, including RBI singles from Erick Aybar and Mike Trout that led to Los Angeles' first two runs in the second inning. A two-run single from Torii Hunter in the seventh extended the Angels' lead to four and ended Parker's evening.
"We knew tonight was going to be a low-scoring game, and obviously with Jered going on the other side, it's one of those things you gotta be a little better and stay locked in those innings and prevent the big inning," Parker said. "I got in hitters' counts, squared up some fastballs and did what they're supposed to do."
"Good hitters get your mistakes, and it looked like every one they threw today, they were opportunistic with key hits," manager Bob Melvin said.
Oakland was never close to touching its counterpart's lead with Weaver on the mound, as the right-hander improved to 5-1 with a 1.02 ERA in his last eight starts against the A's.
"To be honest, extremely frustrating," catcher Derek Norris said of facing Weaver. "I can count five or six times where I fouled a ball right down the middle just straight back. There's something about his deception that throws you off. He has what he has, and that's deception, and it was working for him tonight. Unfortunately, we couldn't get the offense going to support Jarrod."
In three starts and 23 2/3 innings against Oakland this year, Weaver has allowed one run. His support staff -- a group that includes rookie sensation Trout -- isn't half bad, either.
Trout reached base four times Monday night, tallying three stolen bases along the way and garnering a handful of new "fans" from the other side by night's end.
"He fast," Norris said. "One of my better throws since I've been here on his third stolen base, and he still got in there. He's a terrific player. He's really got all five tools, and it's kind of cool to be out there and see him play. Unfortunately, he's on the other side. It's quite fascinating what he's doing."
"He's a good player, and he's playing really well right now, with a lot of confidence, and he's doing everything," Melvin said. "He's hitting for power, he's running fearlessly on the bases. You look at his numbers, and you see he had a pretty prototypical game tonight for the way he's been playing."
The A's wouldn't say as much about their own performance.