Say brehs, will Jay White pull off the biggest Day 1 upset since Devitt in 13'? His match with Okada is the only one from Block A that can qualify as one. On Block B the only candidate is Naito beating the champ, like the good ol' Choshu days.
Here's the list of this "puro tradition" for the G-1
2017: ZSJ beats Tanahashi (IC Champ at the time)
2016: Maru beats Okada and Sanada beats Tanahashi
2015: No big upset though Anderson beats Nakamura in 1st day of block B.
2014: Nothing big. Slight upsets with Yujiro beating Naito and Shibata beating Nakamura.
2013: Devitt beats Okada
2012: Naito beats Nakamura
2011: Nagata beats Tanahashi, MVP beating Nakamura
2010: Naito beats Makabe and Anderson beating Tanahashi
2009: Omori beats Tanahashi
2008: Tenzan beats Kawada (slight upset, though it's Hiroyoshi's only win that year)
2007: Not sure, can't remember if Koshinaka's old ass beating Nakanishi or Millano Collection AT beating Yano could be considered upsets.
2006: No upset, though there's no match that could've triggered one.
2005: Baby Yano (debuting) draws "king of the U-30" Tanahashi.
2004: Shibata beats Chono.
2003: Akiyama beats Tenzan and Yasuda beats Takayama.
2002: Baby Tanahashi (debut) beats Koshinaka. Kenzo Suzuki (debut) beats Yasuda en 37 seconds.
2001: Murakami draws Nagata (eventual winner).
2000: No upset. Lineup for the tournament is fukking abysmal, lol.
1999: Fujinami beats Mutoh (IWGP champ at the time). Single elimination tourney.
1998: Yamazaki beats Fujinami (IWGP champ at the time).
1997: No upset. I don't think Kojima beating Regal would be considered one.
1996: Choshu beats Hashimoto (IWGP champ) in his last G-1. The famous "CHOOOSHUUUUU~!" match and one of the GOAT tourney matches.
1995: Koshinaka beats Mutoh (IWGP champ and eventual winner).
1994: Fujiwara beats Mutoh, Hase beats Hashimoto (IWGP champ)
1993: Hase beats Mutoh, Super Strong Machine beats Koshinaka.
1992: No upset, mostly because it's co-promoted with WCW.
1991: Chono beats Choshu