Siver's mixed martial arts career began in small local shows in Russia and England, amongst other European countries. He fought most frequently for Cage Warriors in England, compiling a 3–1 record.
Ultimate Fighting Championship
After his win against Jim Wallhead at CWFC – Enter The Rough House, Siver was signed by UFC. His debut was against Jess Liaudin at UFC 70 in Manchester, England where he lost via submission (armbar), just 81 seconds into the first round.
Siver was able to bounce back though at UFC 75, again in England. He defeated Naoyuki Kotani via KO (punch) in the second round. This was followed up by a loss to undefeated Gray Maynard at UFC Fight Night 12, via a unanimous decision.
Siver's final match of his first UFC stint was a loss to Melvin Guillard at UFC 86. This fight marked the first knockout loss of Siver's career, which came after just 36 seconds into the first round.
Siver was released by the UFC soon after, having compiled a 1–3 record.
Post-UFC
Siver had his first post-UFC fight at Tempel: Mix Fight Gala VII against Chas Jacquier. Siver won the fight via submission (guillotine choke) at 4.21 of the first round
Return to Ultimate Fighting Championship
This win earned Siver a second shot in UFC. He faced off against Nate Mohr at UFC 93 in Dublin, Ireland. In the third round, Siver was able to TKO his opponent via spinning back kick and punches. This victory was also awarded the Knockout of the Night award.
His second fight was against Dale Hartt at UFC 99, which was the first UFC event held in Siver's home country of Germany. Siver won the fight via submission (rear-naked choke) three minutes into the first round.
Siver then fought Paul Kelly at UFC 105 in Manchester, England and, in the same fashion as his victory over Mohr, was able to TKO his opponent via spinning back kick and punches. Once again, the win earned Siver the Knockout of the Night.[6]
Siver fought Ross Pearson on March 31, 2010, at UFC Fight Night 21.[7] Siver lost the fight via unanimous decision (30–27, 30–27, 30–27). However, the fight won Siver a Fight of the Night bonus.
Siver faced Spencer Fisher on June 19, 2010, at The Ultimate Fighter 11 Finale.[8] Siver won the fight via unanimous decision despite suffering a cut from an accidental headbutt in the first round.
Siver defeated Andre Winner via first round arm-trap rear-naked choke after dropping him with a counter punch at UFC 122, earning Submission of the Night honors.[9]
Siver faced George Sotiropoulos on February 27, 2011, at UFC 127.[10] Siver won the bout via unanimous decision, handing Sotiropoulos his first loss in the UFC. Siver showed excellent takedown defense throughout the fight and picked Sotiropoulos apart on the feet, dropping him twice in the first round.
Siver defeated Matt Wiman on July 2, 2011, at UFC 132 in a very close contest, with all three judges scoring the fight 29–28 in Siver's favor. Siver stated at the post-fight press conference that while the decision was close, that he wouldn't go back and score the fight any differently.[11]
Siver was expected to face Sam Stout on October 29, 2011, at UFC 137.[12] However, it was announced on August 29 that Stout had withdrawn from the bout[13] and was replaced by Donald Cerrone.[14] Siver lost by submission in the first round.
Siver was briefly linked to a rematch with Ross Pearson on April 14, 2012, at UFC on Fuel TV: Gustafsson vs. Silva.[15] However, Siver instead faced Diego Nunes at the event, fighting as a featherweight for the first time in 28 career bouts.[16] He won the fight via unanimous decision.
Siver was expected to face Eddie Yagin on September 1, 2012, at UFC 151.[17] However, after UFC 151 was cancelled, Siver/Yagin was rescheduled for December 8, 2012 at UFC on Fox 5.[18] It was then announced that Yagin had been forced out of the bout due to a sparring injury that landed him in the hospital with swelling around his brain, and was replaced by Nam Phan.[19] He won the fight via unanimous decision.
The bout with Cub Swanson was rescheduled for July 6, 2013 at UFC 162.[22] After a back and forth first two rounds, Swanson defeated Siver via third-round TKO. The performance earned both participants Fight of the Night honors.
Siver faced Manvel Gamburyan on December 28, 2013, at UFC 168.[23] He won the fight via unanimous decision. However, Siver's initial urine sample came back with inconclusive results, which caused the NSAC to test an alternate sample.[24] On March 15, it was announced that Siver had failed his UFC 168 drug test following the testing of second sample came back positive for hCG. As a result, Siver has been suspended by the NSAC and his win over Gamburyan was changed to "No Contest".[25]
Siver was expected to face Robert Whiteford on October 4, 2014, at UFC Fight Night 53.[26] However, Whiteford pulled out of the bout in mid-September and was replaced by promotional newcomer Taylor Lapilus.[27] There was some controversy over the replacement, and the SMMAF subsequently deemed Lapilus an unsuitable opponent, resulting in American Charles Rosa as the last-minute replacement.[28] Siver won the back-and-forth fight by unanimous decision. The bout also earned Siver his fourth Fight of the Night bonus award.[29]
Siver was expected to face returning veteran B.J. Penn on June 4, 2016, at UFC 199.[33] However, Siver was forced out of the bout in early May with an undisclosed injury.[34] The fight with Penn was rescheduled and eventually took place on June 25, 2017, at UFC Fight Night 112.[35] Siver won the fight by majority decision.[36]
Absolute Championship Berkut
Siver opted not to re-sign with the UFC in November 2017, instead signing with ACB.[37]
Siver was set to make his ACB debut on 25 November 2017 at ACB 75 against Martin van Staden, but withdrew due to a shoulder injury.[38]
