For the first round, I'll stick to noting the significant upsets, the results of the U.S. players, and maybe one or two other things as they catch my eye. As the rounds go on and the field is whittled down to manageable proportions, it will be feasible to take a closer look. (Of course, if you spot something of special interest, you can help out in the comments.)
There were a fair number of "half" upsets among the 2700s, with the most notable one being Anish Giri's draw with Ugandan IM Arthur Ssegwanyi, rated 2357. With Black, Giri was winning out of the opening, but allowed his resilient opponent to escape to a drawn ending. Giri charmingly played the drawn ending with an extra pawn and all the pawns on the kingside from move 53 until bare kings on move 158, but despite his hope that his opponent would die of old age, a heart attack or from sheer boredom, Ssegwanyi held the draw. (I'm now rooting for Ssegwanyi to win tomorrow.)
Alexander Grischuk also surrendered a draw to an IM - with White! - giving up half a pawn to Yusup Atabayev of Turkmenistan. Boris Gelfand also gave up a draw with White to an IM (albeit one with a GM rating), one Cristobal Henriquez Villagra of Chile, and oddly enough did so in a winning (but very complicated) position.
Other big dogs giving up draws: Teimour Radjabov (squandering a large if possibly never winning advantage against American Sam Sevian), David Navara (to Tamir Nabaty), Radoslaw Wojtaszek (to Babu M.R. Lalith), Nikita Vitiugov (to Samvel Ter-Sahakyan), Evgeny Tomashevsky (to Ziaur Rahman), Laurent Fressinet (to Ante Brkic), Ian Nepomniachtchi (to Zhao Jun), Michael Adams (to women's world champion Mariya Muzychuk), Dmitry Jakovenko (to Ilia Iljiushenok), and Rustam Kasimdzhanov (to Anton Kovalyov).
That's 13 out of 36, by my count, and there were also two 2700+ rated players who lost. Leinier Dominguez lost to Argentine GM Federico Perez Ponsa while Ni Hua lost to another GM from Argentina, Sandro Mareco.
So it was a very good day for Argentina, and it was also a good day for the host country as Azeri players went +3 =3. The Chinese players had a strong performance as well, despite the aforementioned loss by Ni Hua. Their remaining players went 7-2 (+6-1=2), including a draw by women's #1 Hou Yifan and an upset by Shanglei Lu of former (and near-) 2700 player Alexander Moiseenko.
How about the Americans? In general, they did very well. The big three won, with Hikaru Nakamura and Fabiano Caruana winning comfortably and Wesley So winning...almost comfortably. (There was one hiccup near the time control, but that aside So was generally in charge.) Sam Shankland defeated Ivan Popov, giving the U.S. four first-game winners. We saw above that Sam Sevian stole a draw against Teimour Radjabov, and Alexander Onischuk and Varuzhan Akobian both drew their games as well (against Andrei Volokitin and Viktor Laznicka, respectively). There were two bits of bad news, however, as our #4 and #5 players both lost - and with White. Gata Kamsky was impressively outplayed by Hrant Melkumyan in a Berlin ending, while Robson lost to Yuri Vovk in a Classical French. (It should be noted that Vovk's win was quite attractive, with his 26th move being particularly nice.)
Tournament website here.