The former prime minister of Portugal and head of the UN refugee agency took office on January 1 with a promise to change the United Nations to make it more effective in confronting world crises.
Since then, wars in Syria, Yemen and South Sudan have all taken a turn for the worse, while the administration of US President Donald Trump has imposed the first in a series of potentially crippling funding cuts to the world body.
The UN-brokered peace process however remains in a stalemate.
An unprecedented four famine alerts in South Sudan, Yemen, Somalia and northern Nigeria have overwhelmed UN aid workers, with donor funding falling far short of what is needed to avert mass starvation.
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Compounding the turmoil are North Korea's missile launches, fighting in Libya, tensions over elections in the Democratic Republic of Congo and the world's biggest refugee crisis since World War II.
"He is a much more effective diplomat than Ban Ki-moon, and a much more demanding boss," said Richard Gowan, a UN expert at the European Council on Foreign Relations.
"In a lot of cases, Guterres has been trying to stabilize crises that were running out of control under Ban," he said.
Guterres has travelled to the Middle East, the Gulf region and Africa, personally engaging in behind-the-scenes diplomacy to get leaders to agree on shared priorities for dealing with conflicts.
His reforms focus on cutting costs and streamlining the clunky bureaucracy, matching Haley's calls for the United Nations to show "value for the American taxpayer."
The United States is the biggest contributor to the United Nations, paying 22 per cent of the USD 5.4 billion core budget and 28.5 per cent of the USD 7.9 billion peacekeeping budget.
"The more that Guterres can reform the UN system, the more his relationship with the US will improve," said Martin Edwards, a professor of diplomat at Seton Hall University.
One hiccup however came when the White House blocked Guterres's choice of Palestinian Salam Fayyed to be UN peace envoy for Libya, a setback that highlighted how the UN chief's agenda could be hijacked by the United States.