$Alphabet-C(GOOG.US)$ and its rivals are wielding a new weapon in the battle for cloud-computing market share: big-dollar investments in companies that agree to sign on to their services.

With Thomas Kurian serving as cloud chief executive since 2019 after a long tenure at $Oracle(ORCL.US)$, the Alphabet Inc. unit has been tapping its $142 billion treasure chest of cash to make it more attractive to customers. Google has taken equity stakes over the past year in companies including Univision Communications Inc. and $CME Group(CME.US)$, in turn winning multiyear commitments to its cloud service worth as much as $1 billion or more.

The deals make Google among the most aggressive of several big companies seeking to gain ground on $Amazon(AMZN.US)$, the cloud market leader. $Microsoft(MSFT.US)$ has also taken stakes in several startups as part of deals that entail them using its cloud. And Oracle last year tried to buy a major stake in TikTok as part of a deal to have the China-owned social media app use its cloud service -- and cited the boost to its cloud business this month in announcing its biggest deal ever, the planned $28.3 billion acquisition of the medical-records company $Cerner(CERN.US)$.

The nascent strategy has helped Google boost its market share in a huge and rapidly expanding industry that is key for its growth. Google now claims 6% of the cloud market, up 1 percentage point from a year earlier, though still far behind Amazon's 41% share and Microsoft's 20%.

"No one wants to do this 'buying' customers, but if you're No. 3 or 4, you have to be creative," said Holger Mueller, an analyst at Constellation Research Inc. who focuses on enterprise technologies.

The investments underscore how tech companies' robust cash flows give them a big edge over smaller competitors in selling cloud infrastructure services, the core business of providing rented, remote computing power and storage. Those companies can afford the huge infrastructure investments necessary to build multibillion-dollar data centers and subsidize the costs of moving clients to their cloud systems -- helping explain why three companies control two-thirds of the market.

A Google Cloud spokesman said that it has largely won customers with its capabilities, adding that investments are part of their strategy. "In certain instances, Google pursues investments and partnerships in attractive growth areas, which is a common practice across many companies within the enterprise industry," he said.

Alphabet investors see Google Cloud as its most promising growth area and best chance to diversify beyond the online advertising business that accounts for 80% of sales. The cloud unit, which began disclosing financials in 2020, recorded more revenue in the first nine months of 2021 than for all of 2020, and is expected to grow 50% to $19.26 billion for the full year.

Those gains have carried high costs, with the company spending aggressively to develop infrastructure and expand its sales team. Google Cloud in the January-September period halved its operating loss from a year earlier, to $2.2 billion.

Google's deals have covered customers in a range of sizes and sectors. In the span of a little more than a year, it has invested $1 billion in the futures-exchange company CME Group; $450 million in the home security provider ADT Inc.; and undisclosed sums in the Spanish-language media company Univision and the healthtech startup Tempus Labs Inc. All have signed long-term cloud computing contracts with Google.

Mr. Kurian has played a central role in ushering in the investment strategy, said former Google Cloud executives. Before his arrival from Oracle, Google made a priority of developing new technologies to lure customers over traditional sales. He revamped its approach, adding sales staff and sweetening performance bonuses.

Microsoft announced an investment and cloud deal with the food-delivery startup $Grab Holdings(GRAB.US)$ in 2018. Mr. Kurian floated the idea of adopting a similar strategy to catch up with its rivals, former Google Cloud executives said. The investments were designed to give companies another reason to choose Google over rivals and convince them that Google was financially committed to developing technologies to benefit their businesses.

Microsoft has continued leveraging investments into emerging startups to strike cloud partnerships, with one of its largest bets being a stake in $General Motors(GM.US)$'s driverless-car startup, Cruise. Under terms of the deal, Cruise will use Microsoft's Azure cloud-computing platform to roll out its autonomous-vehicle services.

As Microsoft proceeded, Google followed suit, taking part in a $200 million investment round for Chicago-based Tempus, which uses artificial intelligence to improve patient care. As part of the 2020 investment, Google offered significant discounts for Tempus to move to its cloud from Amazon, said a person familiar with details of the deal.

Under the contract, Tempus agreed to spend at least $20 million in the first year on Google Cloud, the person said, meaning Google's revenue from the deal could exceed its investment within a few years.

Tempus didn't respond to requests for comment. Univision's chief executive said Google's investment was a corporate negotiation separate from the cloud agreement but called Google a true partner committed to evolving its business.

The search company took a broader approach with its partnership with ADT. In 2018, the home security firm was looking to move some of its on-premise data to the cloud, said Don Young, ADT's chief operating officer. It met with representatives from Google who eventually proposed a deal that went beyond cloud computing to include a partnership between ADT and Google's Nest smart-home business as well as a $450 million investment in ADT.

Mr. Young said ADT would have placed some data in Google Cloud regardless of the investment but added that the company has increased its spending on Google's cloud services since then.

"We would have done a cloud deal, yes," Mr. Young said. "But the exact cloud deal we did? I'm not sure."

During negotiations to move its trading system to Google Cloud, CME Group Chief Executive Terry Duffy made an investment in his firm key to a deal. "I wanted a partner, not just a cloud provider," Mr. Duffy said in an interview.

Mr. Kurian said at the time: "The equity investment is a representation of our commitment." He said it ensured Google would assign its best people to support CME Group's cloud efforts.