Ronaldo's eighth-minute header in Moscow gave Portugal their first win in the tournament and victory over New Zealand on Saturday would secure a semi-final spot.
Goals from Peralta and Raul Jimenez saw Mexico move top of Group A later in the day, above Portugal on goals scored, and knock New Zealand out of the competition.
Ronaldo let his football do the talking after the recent tax-evasion accusations that have left his Real Madrid future uncertain, with his second man-of-the-match performance following Sunday's 2-2 draw with Mexico.
"We're very happy, it's the first time Portugal have won in Russia. The team played very well against a side playing at home with the support of their fans. But we were better, we had more chances," he said.
Ronaldo is accused by Spanish authorities of having evaded paying 14.7 million euros (USD 16.5m) in tax and has been summoned to appear in court next month in Madrid.
But he was all smiles, escorting a young mascot in a wheelchair out onto the Moscow pitch before netting his first Confederations Cup goal.
"He was hospitalised and we think he broke his leg," said Portugal coach Fernando Santos.
Guerreiro's towering cross from the left flank hung in the air and found Ronaldo, who rose at the far post to head back across Igor Akinfeev.
Only a superb one-handed reflex save from Akinfeev, who made his 100th international appearance, stopped Andre Silva's bullet header just after the break.
The hosts were unlucky not to force an equaliser after a string of chances in a strong second-half display. Defender Georgy Dzhikiya headed narrowly over the bar from the game's final corner in added time.
===================================
Later on Wednesday, Mexico needed second-half goals by Benfica's Jimenez and Peralta to grab victory over New Zealand in a bad-tempered match at Sochi.
Juan Carlos Osorio's side now just need a draw against Russia in Kazan on Saturday to be sure of reaching the semi- finals.
The Kiwis' superb first-half display and Chris Wood's shock goal rattled Mexico and a tense match boiled over with a mass brawl in the dying stages. The match turned when Porto midfielder Hector Herrera came on for the second half and Mexico's attacks started to flow.
New Zealand coach Anthony Hudson had vowed they would bounce back after Saturday's opening 2-0 defeat by Russia and his team were true to his word.
"Everyone is incredibly disappointed in the changing room and we feel we should have got more," said Hudson.
The Oceania champions took a shock lead when Clayton Lewis threaded his pass between two defenders to Wood, who coolly fired home on 42 minutes.
Mexico equalised when Aquino broke down the left flank and passed to Marco Fabian, who squared for forward Jimenez to fire home on 54 minutes.
And Peralta hit the winner in the 72nd minute when Aquino pulled the ball back for the 33-year-old to find the net.
Disclaimer: No Business Standard Journalist was involved in creation of this content
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
