As Democrat Joe Biden - an avowed multilateralist - prepares to replace Donald Trump as US president in two months, the G20 statement struck a bolder tone on global trade, climate change and the role of the World Health Organization.
The leaders are huddling online for the two-day "gathering" as global efforts intensify for a large-scale rollout of coronavirus vaccines after a breakthrough in trials, and as calls grow for G20 nations to plug a $4.5-billion funding shortfall.
Her words were echoed by French President Emmanuel Macron, who also adressed leaders.
"I am confident that the Riyadh summit will deliver significant and decisive results and will lead to adopting economic and social policies that will restore hope and reassurance to the people of the world, " King Salman said.
Despite having to abandon much of the usual summit pageantry, Saudi Arabia launched the meeting with an aerial acrobatics display over Riyadh.
The gathering brought backlash from Saudi and worldwide human rights groups - as well as some USA and European lawmakers - calling on world leaders to boycott or downgrade their representation over the kingdom's abuses, including jailings of women activists and the killing of Washington Post contributor Jamal Khashoggi at the Saudi Consulate in Istanbul in 2018.
It was initially unclear if Trump would attend, though on Friday he announced he would.
Along with Xi, German Chancellor Angela Merkel and Russian President Vladimir Putin are among leaders expected to speak at the summit, with climate change among the issues topping the agenda, sources close to the organisers said.
European members of the G20 are likely to push for more.
Bolsonaro, who spent months downplaying the severity of the virus while deaths mounted rapidly inside Brazil, emphasized in a video message that world leaders "should take care of people's health and of the economy at the same time".
However, G20 leaders face mounting pressure to help stave off possible credit defaults across developing nations.
Last week, the bloc's finance ministers declared a "common framework" for an extended debt restructuring plan for countries hit hard by the virus, but campaigners say the measure is insufficient.
The G20 launched the DSSI in April to address the immediate liquidity needs of low-income countries, allowing the debt service payments due from May 1 to the end of the year owed by the most impoverished countries to be suspended.
The European Union wants the G20 to invest $4.5bn (€3.7 billion) to help, as well as agreeing new global standards for tackling pandemics.
The programme promotes an equitable distribution of Covid-19 vaccines to rein in the pandemic.
"Investors are not journalists, investors are looking for countries where they can place their trust in an effective government that has proper economic decision-making", he said. It's the first time an Arab nation has hosted the meeting, and campaigners see it at an opportunity to draw attention to the plight of jailed human rights defenders in the country.