As the front-runners jostled for position off the line, Hamilton had to take to the grass to avoid running into the back of Vettel, who was trying to get into the slipstream of his polesitting Ferrari team-mate Charles Leclerc.
Hamilton emerged victorious after making a dicey one-stop strategy work with ease, holding off Vettel to the end, but the Mercedes man said things could have been terminal for both not long after launching.
"I actually got a really good start," Hamilton said.
"So I was pulling up to Charles and Seb is coming across, coming across, coming across and I'm thinking 'I'm on the white line, I don't have anywhere further to go'. And he just keeps coming.
"So I had to avoid crashing with him, going on the grass. Avoid his wheels as well, otherwise I could have caused a big collision for him."
Hamilton was not able to avoid a tangle with Max Verstappen just a few metres later, with a run across the grass at Turn 2 dropping both drivers down the order, although it was more costly for the Dutchman.
"Then I was surrounded by a bunch of cars, I braked into Turn 1, and all of a sudden Max is alongside me," Hamilton said.
"If you've seen races before, I always leave Max a lot of space – it's the smartest thing you can do.
"But there wasn't a lot of space to give him space. I think he had an oversteer moment or something and then I got a massive hit from behind."
When Vettel asked Hamilton for further details he added: "We were going through the corner, you were about to go into Turn 2, my back end came out and I nearly took you out and then we went straight over the grass. It was hair-raising!"
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