Well it is not like it had any marketing, or anticipation before it was available to buy.

Quite a few games of the time got pretty pessimistic outlooks in retrospect. Super Smash Bros, like I mentioned before, but also the original Warcraft and Command & Conquer games vastly outsold what their publisher had hoped (and kickstarted the RTS genre). Still, Tomb Raider is a good example due to how big that gap is

While we're at PC games, Wolfenstein 3D, Duke Nukem 3D and Doom could count, having started their lives as Shareware titles but having got full retail releases due to their immense successes (besides poplarizing the FPS genre and bringing it to the masses).

Rocket league and PUBG

Wait are you trying to imply that: when games don't have high levels of pressure to perform, they often do well?
Someone better tell that to: EA, Ubisoft and Square Enix.

It would also be wise to look at mods such as: Gmod, The Stanley Parable and DayZ.

Edit:
To anyone who hasn't yet done so, play: The Stanley Parable.

Brain Age - The original sold under 28 thousand copies its first week in Europe. It ended up selling over 9.2 million in Europe alone, a 300-fold increase.

Demon's Souls - Only sold 410,000 in 2009, when it launched in Japan and America, but eventually reached 1.83 million, thanks to better sales in 2010 and 2011 and over 100k in both 2012 and 2013. The game reached 892k in the USA alone, after only 53k sales on Week 1.

Five Nights at Freddy's - The original Kickstarter raised exactly $0.00.

Katamari Damacy - The game that launched a franchise had 35000 sales its first week in Japan.

Zumba Fitness - The Just Dance of Wii Fitness games. 36k at launch in America, over 3.1 million lifetime American sales.

stikk it sold great out of the gate especially since the majority of h1z1 br players jumped on it.

it didnt need any marketing other that being a steam bestseller nonstop.

Games I think of as sleeper hits: Demon's Souls, Katamari Damacy, ICO, Ultima Online, Civilization, Diablo. (These don't really fit all of the criteria in the first post though.)

Games that do fit that critera: 1) Tomb Raider - Mostly a sleeper hit, because the PS1 was kind of a sleeper hit of a console, and it was released before the huge FFVII media push.

2) World of Warcraft - Was well known by MMO gamers before it released, but this was a relatively small group of people. Also most of them didn't go over to play World of Warcraft (me included). On the other hand it found a gigantic new audience of people who knew nothing of MMO's.

@bold not really. CoD sold very well in Japan before Splatoon. And that game is only a 3rd party western game.

@OP other then those that have been said, I would say Halo and Gran Turismo fit the bill. I don't know early sales, but they ended up becoming the biggest franchises respectively for MS and Sony from the get go with the success of their first games. Especially for new ips, is very likely to be sleeper imo.

I guess GT did launch big and Halo was a launch title though. Still amazing for new ips.

Splatoon and the first Yo-kai Watch (only in Japan tho).

Final Fantasy VII
Pokemon Red and Green/Red and Blue
Minecraft
Wii Sports
Tomodachi Life
PlayerUnknown's BattleGrounds
Super Smash Bros.