"They probably haven't had the expectations that they have this year. Coming in new to the club, the thing that has shocked me is how tense everyone is," Murphy said after the listless Padres were shut out for the second straight game by the Seattle Mariners, 7-0 on Wednesday.
Cano had four hits and drove in three runs. Cruz connected for his 20th homer on his 35th birthday.
Walker (7-6) struck out seven and walked none. The 22-year-old righty combined with four relievers on a three-hitter.
Rookie Mike Montgomery threw a one-hitter against the Padres on Tuesday night. They have been blanked 13 times this year.
That cost manager Bud Black his job as manager on June 15. The Padres are 5-9 under Murphy, a former Triple-A manager and college coach.
Murphy said it's been "an eye-opening learning experience."
"Guys not trusting their own ability. Guys not trusting themselves. Guys not knowing how good they are. Guys not knowing how capable they are. Guys letting the outside expectations affect them," he said.
"We have work to do as an offensive club. There are no breaks. We are going into a pretty significant road trip. This one hurts, yesterday hurt. These two put an accent on some things we need to work on," Murphy said.
"It's frustrating because no one likes to lose, especially the way we lost," Upton said. "We're not getting any hits, we're not scoring any runs. It's frustrating for all of us and we have to figure out a way to do better.
"We should have high expectations for ourselves. The second we feel like we're allowed to play mediocre, then that's when it's going to make this team really, really bad. It's July first and we have to do better than we are doing. The second half of the season is coming up fast and we need to get on track."
Shields (7-3) failed for the fifth time to get his eighth victory. He's lost three straight starts.
Cano hit an opposite-field homer to left leading off the sixth. His fifth home run came after he'd been 0 for 10 with four strikeouts in his last three games.
Cano improved to 37 for 90 (.411) lifetime against Shields, with five homers and 16 RBIs. The 37 hits are the most by an active player against an active pitcher.
Shields was pulled after walking the bases loaded with two outs in the seventh and Cano greeted Frank Garces with an RBI single. Dustin Ackley, who had pinch-hit for Walker, was thrown out trying to score from second.
Cano hit an RBI double off Kevin Quackenbush with one out in the ninth. Cruz followed by greeting Marcus Mateo with a two-run shot to left.
Walker's winning streak includes four road starts during which he's allowed just three runs in 26 innings.
Solarte doubled with one out in the seventh inning Tuesday night for San Diego's only hit against Montgomery.
Shields allowed two runs and four hits in 6 2-3 innings, struck out seven and walked four. The Padres have scored only three runs in his last four starts.
Padres: INF Will Middlebrooks is still day-to-day with an ankle injury, although he remains available for pinch-hitting duty.
Mariners: Seattle continues its nine-game, three-city trip when it opens a four-game series at Oakland on Wednesday night, with LHP Roenis Elias (4-5, 4.25) scheduled to start against LHP Scott Kazmir (4-5, 2.79).
Padres: San Diego starts a 10-game, three-city trip that takes it to the All-Star break. RHP Tyson Ross (5-7, 3.57 ERA) is scheduled to start the opener of a four-game series at St. Louis on Wednesday night.