First matches your mmr is very sensitive. You start at 1200ish mmr, corresponding to silver 4ish, and so you'll play players at around that level. If you win that match, your mmr goes up some, so you might play again in a silver 3ish match. If you win again, you'll be in a harder match and so on. If you win all 10 solo, you're likely to be playing with golds at the end.
You can rig things slightly if you have a high mmr friend to duo with so you can play harder matches for greater mmr gains, so for example challenger smurfs sometimes duo with high mmr other smurfs and manage to place plat 5 even on a fresh account. Even in that scenario they won't face diamonds on a fresh account though.
Note that your teammates are going to be of a similar mmr in each match as your opponents, so if you actually are winning those matchs due to your own skill things should remain relatively fair.