Those risks and other risks are described in the company's filings with the Securities and Exchange Commission over the last 12 months.
I'm pleased to report that for the quarter, Group one generated adjusted net income of $103 million.
This equates to adjusted earnings per share of $5.57 per diluted share, an increase of 236% over the prior year and an increase of 170% over the pre-pandemic first quarter of 2019.
Our adjusted net income results exclude noncore items of $1.7 million of after-tax disaster pay provided to employees who couldn't work during our February Texas store closures partially offset by an $800,000 after-tax benefit from legal settlements and a $200,000 after-tax net gain on dealership and real estate transactions.
These profit results were particularly impressive given the fact that our Texas operations, which typically represent around 40% of our total revenues, were severely impacted due to a record-setting February winter weather event.
This improvement was driven by new and used vehicle revenue increases in the U.S., of well over 20% in the first quarter.
On a same-store basis, our U.S. total aftersales gross profit increased 3% versus the first quarter of 2019, and customer paid gross profit increased 14% over that same pre-pandemic time period.
Despite not having the benefit of physical sales departments, or the ability to conduct test drives, we were able to deliver over 13,000 new and used vehicles during the quarter.
Limited new vehicle availability increased our same-store new vehicle margins by 160 basis points to 5.6% during the first quarter.
Our aftersales margin increased by almost 400 basis points to 58.4% as most service work at our dealerships was heavy repair work as customers chose to defer routine maintenance until after the lockdown.
The strong new vehicle and aftersales margins combined with strong cost discipline, evidenced by an 1,800 basis point same-store SG&A improvement over last year, enabled us to generate a meaningful level of profit in the U.K. despite closed showrooms.
This gives us a high level of confidence in our U.K. business during the remainder of 2021.
Compared to the pre-pandemic first quarter of 2019, our same-store new and used unit sales increased by 11% and 5%, respectively.
This 11% increase in new outperformed the retail industry.
U.S. new vehicle inventory levels finished the quarter at 14,500 units, of 34 days supply.
Our same-store used vehicle unit sales improved sequentially by 14%, along with a 5% growth over the first quarter of 2019.
Although we are around record high monthly levels of 90 units sold core rooftop, in the quarter, we continue to believe there is a great deal of opportunity in used vehicles in our dealerships going forward.
As Earl mentioned, our same-store CP customer pay gross profit was up 14% versus the first quarter of 2019.
This allowed us to grow total aftersales gross profit by 3% versus pre-pandemic levels, despite the significant headwinds in warranty and collision, both of which will reverse in time.
In March, traffic counts increased and our same-store customer pay RO count grew 23% versus March of 2020.
Our first quarter adjusted SG&A as a percentage of gross profit was 63%, down from 74% in the pre-pandemic first quarter of 2019.
We continued our upward trajectory in the first quarter by selling a record 4,000 vehicles through Acceleride, an increase of 124% over the prior year and 7% of total retail units sold.
Despite a 7% decline in new vehicle industry sales driven by tight inventories and additional COVID lockdowns, our team did a tremendous job of growing margins and aggressively thinning the cost structure in order to realize a very strong quarterly profit in what is seasonally the weakest quarter of the year.
We easily set a record for the most profitable first quarter over the entire eight years of Group 1's ownership and are well positioned to benefit from a sales rebound coming out of the pandemic.
As of March 31, we had $83 million of cash on hand and another $245 million invested in our floorplan offset accounts bringing total cash liquidity to $328 million.
There was also another $283 million of additional borrowing capacity on our U.S. syndicated acquisition line bringing total immediate liquidity to over $600 million.
We also generated $157 million of adjusted operating cash flow in the first quarter and $134 million of free cash flow after backing out capex.
On a net basis, which considers all U.S. cash on hand, our leverage was 1.6 times as of March 31.
Our quarterly floorplan interest of $7.6 million was a decrease of $5.3 million or 41% from the first quarter of 2020.
Non-floorplan interest expense decreased by $4.3 million or 24% from prior year, primarily due to the last year's bond debt refinancing.
We have floorplan swaps averaging $550 million in place through 2026.
We also considering our mortgage swaps on bond debt, over 75% of our debt is at fixed rates.
As a result, a 100-basis point increase in interest rates would only have an approximate $0.20 negative impact on our annual EPS.
Related to our corporate development efforts, we previously announced the March acquisition of two Toyota franchises on Cape Cod that increased our new England platform to 10 stores and will contribute $120 million in incremental annual revenues.

Summary:
This equates to adjusted earnings per share of $5.57 per diluted share, an increase of 236% over the prior year and an increase of 170% over the pre-pandemic first quarter of 2019.
This improvement was driven by new and used vehicle revenue increases in the U.S., of well over 20% in the first quarter.
This gives us a high level of confidence in our U.K. business during the remainder of 2021.
Non-floorplan interest expense decreased by $4.3 million or 24% from prior year, primarily due to the last year's bond debt refinancing.