By Anirban Sen

NEW YORK (Reuters) – Dealmakers at Simpson Thacher & Bartlett are riding high.

They worked on the three biggest mergers and acquisitions (M&A) announced so far this year, pushing Simpson Thacher to the No. For the first time since 17 years, Simpson Thacher occupied the #1 spot on the U.S. dealmaking league table for law firms.

Veteran M&A lawyer Alan Klein, who has advised Microsoft Corp (NASDAQ:), on each major acquisition in the past decade. But the largest deal of this year so far was the announcement by the tech giant that it would buy Activision Blizzard Inc. (NASDAQ:). The transaction, valued at $68.7billion, is the most significant.

Klein was brought in as an advisor. Twitter Inc (NYSE:)’s board of directors alongside another law firm, Wilson Sonsini Goodrich & Rosati, when Elon Musk negotiated a $44-billion deal last month to acquire the social media company.

Atif Azher is a Klein’s Simpson Thacher Partner. He has advised on many large transactions, including the $67 billion acquisition by EMC (NYSE 🙂 of data-storage firm Dell Technologies Inc. Pfizer Inc (NYSE) buys pharmaceutical peer Wyeth for $68 Billion – Silver Lake advised the private equity firm Silver Lake on the 61-billion sale (NYSE) of cloud-software VMware to Broadcom (NASDAQ) Inc.

This is an incredibly fortunate and remarkable achievement to have three deals in excess of $40 billion, with two exceeding $60 billion each, within five months. Klein said that it would have been extraordinary to be involved in these deals within a single year.

While Simpson Thacher has consistently ranked among the top ten most-active law firms in U.S. M&A, it has not finished a year as No 1 since 2005. This year it is on pace to achieve that feat. It has advised on deals totaling $230 billion this year. More than any other law company. It is trailed by Skadden, Arps, Slate, Meagher & Flom, which has advised on $193 billion worth of deals.

Anthony Vernace from Simpson Thacher was also a Simpson Thacher Partner and worked alongside Klein on Activision’s and Twitter’s deals. Vernace said that Simpson Thacher’s long-standing relationships with Microsoft and Silver Lake were key in helping them beat out top-drawer U.S. legal firms to take the leading roles in those transactions.

Vernace stated that each of these transactions is the result of the long-standing client relationships and broad experience we have.