Rankings and seeds are certainly insightful when it comes to getting a snapshot of the contenders for any Grand Slam. However, it's often the case that there are dangerous non-seeds in any major, players who are dangerous but have not played well enough over the last 52 weeks to get a seed. These kinds of players get plopped down in the draw at random points, and they could certainly mess things up in the early rounds, even for the best players. Ivo Karlovic and three others are such players heading into the 2017 Us Open.

Karlovic looks to duplicate last year's success

Karlovic heads into the tournament in decent form, and he is one player that many would prefer not to see in the opening rounds. With an amazing service game, Karlovic has enjoyed some success on the faster surfaces over his career. Last year he made the fourth round at the US Open, and he enters this year's US Open with wins recently over seeded-players Jo-Wilfried Tsonga (No. 8) and Marin Cilic (No. 5), the latter of which Karlovic beat on grass ahead of Cilic's amazing run at Wimbledon. The Croat may be 38 years old, but so long as he can dial up his aces he can keep the points short, and he can prove dangerous.

Two dangerous, likely qualifiers

Leonardo Mayer is another dangerous non-seed that should be in the draw. The Argentine is in the final round of qualifying ahead of the US Open. Should he fall at the last hurdle of qualifying, Mayer is still a candidate for the main draw. As the top seed in qualifying in the final round, he would be a lucky loser at Flushing Meadows.

Having won Hamburg not long ago, Mayer is on top of his game, and he is more than capable of knocking out the middle seeds. A player with a recent 500-series title will have the attention of all in his path, and no high seed will like seeing Mayer's name near them in the draw.

Denis Shapovalov is also at the final stage of qualifying.

The Canadian, like Mayer, would be in the main draw via his ranking if he had ascended a little earlier in the season. Shapovalov, following his amazing Rogers Cup, has recent victories over three players that are seeded at the US Open. He beat Rafael Nadal (No. 1), Juan Martin del Potro (No. 24), and Adrian Mannarino (No. 30). If Shapovalov makes the main draw where he falls will be very interesting for his chances. If he ends up sharing a draw to the fourth round with anyone seeded outside of the top-ten players, then the Canadian may very well make the fourth round himself. He's certainly a dangerous player, and you'd think that many would prefer that he go out in the last hurdle of qualifying at this point.