NEWPORT BEACH, CA, USA -- After a topsy-turvy tournament with tons of upsets, the Oracle Challenger Series event in Newport Beach will conclude with two unseeded players in the championship match.

On Saturday, wild card Danielle Collins of the United States took out the final seeded player left standing, No.7 seed Ajla Tomljanovic of Croatia, 6-4, 6-3, while Russian qualifier Sofya Zhuk turned around her match against fellow qualifier Mayo Hibi of Japan to claim victory, 2-6, 7-6(7), 6-4.

Collins and Zhuk will face off on Sunday in the biggest final of each of their careers, to determine which of the two will claim the first WTA 125K Series event of the 2018 season. Collins also has her sights set on being awarded a wild card into the 2018 BNP Paribas Open, which is granted to the top American finisher in the two Oracle Challenger Series events.

Also on Saturday, Misaki Doi of Japan and Switzerland's Jil Teichmann paired up to claim the doubles title, overcoming American Jamie Loeb and Rebecca Peterson of Sweden, 7-6(4), 1-6, 10-8.

In a semifinal between two 24-year-olds, Collins moved past Tomljanovic in a hard-hitting 77-minute match, where Collins had three aces (to Tomljanovic's none) and won 84 percent of points on her first serve.

The American took the early lead, breaking for 2-0, before the Croatian broke Collins for the only time in the match to get back on serve at 4-3. But a long final game of the first set went the way of Collins, as consecutive forehand errors by Tomljanovic allowed the wild card to break for a 6-4 lead on her fourth set point.

Read more: Tomljanovic mounts comeback to make Newport Beach semis

Both players were serving well and hitting strongly off both sides throughout most of the second set, and there were no break points for either through the first seven games.

But a double fault by Tomljanovic at 4-3 gave Collins a 15-30 edge, and the American crushed a service return on the next point to force an error and set up double break point. Collins claimed the 5-3 lead when a Tomljanovic forehand went wide, and she held at love in the next game with a forehand winner, thereby advancing to the final.

The other semifinal was a very different encounter, as Zhuk and Hibi used a remarkable variety of shot and pace before the 18-year-old Russian outlasted 20-year-old Hibi in a gruelling two hours and 34 minutes. The two players were nearly evenly matched on serving statistics, and Zhuk got the better of Hibi only during the final two games of the match.

Hibi took the first set with ease, as Zhuk struggled early with the Japanese player's deep and well-placed backhand slices. Hibi deployed that shot constantly, drawing errors from the Russian en route to a quick opening frame.

Read more: Collins survives a tough day for Americans at Newport Beach

The second set was less straightforward, as the combatants broke each other three times apiece on the way to 4-4. But Zhuk figured out the best way to combat Hibi's unorthodox game, hitting high balls to lower the chances of Hibi sending back a slice, and then striking a forehand winner when she could.

Hibi, to her credit, saved two set points on her serve at 4-5, holding for 5-5 with a drop shot winner. She then broke Zhuk to take a 6-5 lead and serve for the match, but was unable to see a match point before being broken back, moving the players into a tiebreak.

Read more: Hibi stuns Riske in Newport Beach opener

In the breaker, a well-played backhand down the line gave Zhuk a 6-3 lead and three set points, but Hibi survived them all to get to 6-6. Hibi saved a fourth set point on her serve at 6-7 before a backhand crosscourt winner by Zhuk gave her the coveted mini-break at 8-7. On her fifth set point, the Russian received a gift with an unforced error off of a Hibi overhead, tying the match after two hours of play.

The third set featured strong all-court play by both Hibi and Zhuk, and they advanced to 4-4 with no struggles for either. In that game, though, Zhuk claimed the first break point of the set with a forehand winner, and broke for 5-4 with a backhand winner off a Hibi drop shot. Zhuk closed out the battle of the qualifiers in the very next game on her first match point.