Sears was coaching Ana Ivanovic on Rod Laver Arena as she faced American Madison Keys in the night session but proceedings came to a halt when the 58-year-old collapsed with Ivanovic leading 6-4 1-0.
At first it was thought a spectator might have taken ill -- that's happened already at the tournament as Ivanovic played -- but it was instead Sears who was in distress.
He could be seen leaving the center court on a stretcher and was taken to hospital. Ivanovic, a former world No. 1, was in tears as she looked on. Keys, a semifinalist in 2015, and Ivanovic stayed on court for about 10 minutes before leaving.
All this happened while Murray faced Portugal's Joao Sousa in another stadium, Margaret Court Arena. He appeared to be unaware of what was transpiring at Rod Laver Arena.
Murray is married to Kim Sears and the couple are expecting their first child in the second week of February. Kim Sears was in the UK.
Murray's brother, Jamie, a doubles player, brought positive news surrounding the health of Nigel Sears when he said near the locker room: "I think he's going to be okay."
According to Jamie Murray, Nigel Sears was conscious and talking.
Ivanovic and Keys returned to the court about an hour after Nigel Sears collapsed and the tournament later released a statement.
"A male in his 50s fell ill in Rod Laver Arena this evening," the statement said. "He was transported to hospital by ambulance.
"The match was suspended and the players updated on his condition. The players had the opportunity to consult with their teams and then went back on court."
Besides working with Ivanovic, Sears has coached Slovakian veteran Daniela Hantuchova, retired former top-10 player Amanda Coetzer and he was formerly the head of women's tennis at Britain's Lawn Tennis Association.
Murray won his match but, contrary to the norm, wasn't interviewed on court. The mandatory post-match news conferences were canceled for Murray, Keys -- who rallied to defeat Ivanovic in three sets -- and Ivanovic.