In March 2020, the World Health Organization declared the rapidly growing COVID-19 outbreak a global pandemic. On March 16, 2020, in an effort to contain the virus, the state of Colorado mandated a temporary shutdown of all casinos including Monarch Black Hawk and, on March 17, 2020, the state of Nevada mandated the temporary closure of all casinos including the Atlantis in Reno. Our Nevada and Colorado properties partially reopened with limited operations on June 4, 2020 and June 17, 2020, respectively. Therefore, the nine-month periods financial results comparison set forth below should be read with the 2020 partial period closures in mind.
Following the reopening of our operations and through the three- and nine-month periods ended September 30, 2021, we continued to operate under government-imposed capacity restrictions on our operations and various COVID-19 safety protocols. We were continually adjusting our operations to the restrictions in occupancy and social distancing requirements, which included reduced seating at table games and in all restaurants, and a decreased number of active slot machines on the casino floors. The convention business at Atlantis was adversely affected by the state-mandated gathering limits. We have experienced hotel stay and convention booking cancellations, and since the reopening, guest visitation and hotel and convention bookings have been inconsistent.
Our financial results for the three and nine months ended September 30, 2020 were significantly impacted by the unprecedented government-mandated closure of our Nevada and Colorado properties in response to the COVID-19 pandemic, which lasted approximately three months, and the related operational changes to comply with government restrictions as well as changes in customer demand and overall travel and leisure industry.
Despite a strong reopening, we are operating in an environment of high uncertainty and there may be additional government restrictions placed on all of our services, such as gaming, restaurants, spas and salons, entertainment venues and convention and meeting space, which could lead to lower demand and revenue. Such restrictions could also increase our costs, further decrease our operating margins and have a material adverse effect on our operations, cash flows and financial results.
A new Delta variant of COVID-19, which appears to be the most transmissible variant to date, has been spreading globally. In July 2021, due to reports of increased COVID-19 cases apparently driven by the new Delta variant, Nevada state government officials reintroduced mask mandates for all persons in certain public indoor locations, including casino resorts such as the Atlantis. Colorado officials may do the same. These new developments, and any increased restrictions on operations, may adversely impact our results of operations.
While we have incurred significant disruptions from the COVID-19 outbreak, we are unable to accurately predict the full impact that COVID-19 will have due to numerous uncertainties and the dynamic nature of the circumstances, including the duration and severity of the disease, the possibility of the outbreak levels seen to return, the long-term impact on demand following the reopening of our casinos, and other actions or restrictions that may be taken by governmental authorities, the impact thereof to the general U.S economy and to our customers. We will continue to evaluate the nature and extent of the impact to our business, results of operations, and financial condition.
Monarch Casino Resort Spa Black Hawk expansion
Our financial results for the three and nine months ended September 30, 2021 benefited from the phased opening of operations at our newly transformed Monarch Black Hawk, which opening started in the fourth quarter of 2020. Monarch Black Hawk operations continue to ramp up. The new hotel, including a spa and pool on the top floor, are fully opened. On May 14, 2021, we opened our new poker room. With the opening of our expanded casino floor, we had increased the number slot machines by approximately 190 and table games by 10, compared to the pre-COVID active gaming devices at Monarch Black Hawk.
Comparison of Operating Results for the Three-Month Periods Ended September 30, 2021 and 2020
For the three months ended September 30, 2021, our net income totaled $22.3 million, or $1.15 per diluted share, compared to net income of $10.7 million, or $0.57 per diluted share for the same period in 2020, reflecting a 107.7% and 101.8% increase in net income and diluted earnings per share, respectively. Net revenues in the three months ended September 30, 2021, totaled $111.6 million, an increase of $51.8 million, or 86.5%, compared to the three months ended September 30, 2020. Income from operations for the three months ended September 30, 2021, totaled $29.0 million compared to income from operations of $13.4 million for the same period in 2020.